I haven't automated a reproducer, but I have a reproducer for the proximate cause of the issue, which is related to behavior in RGWRados::Bucket::List::list_objects_ordered (as it's known now that there is a distinction between ordered and unordered listing).
A 2014 change in the ancestor of this method introduced logic which attempts to conditionally advance the marker returned from CLS, if the listing uses delimter and marker contains an instance of prefix. The logic updating marker uses decode_ and encode_utf8 to obtain a string "after" delimiter lexically--but incrementing the numeric value of marker as written generally doesn't work as expected--in particular, decode_utf8 doesn't actually take arbitrary utf-8 sequences in the manner the code expects. After discussion, I'm inclined to avoid changing marker altogether, assuming it can be proved the enumeration will terminate. IIUC (not a certainty), this is an optimization only (attempt to prove by construction below).
[mbenjamin@lemon python]$ ./boto3_delim.py
booger1_o/0
booger1_odelimstr0
booger1_o/1
booger1_odelimstr1
booger1_o/2
booger1_odelimstr2
booger1_o/3
booger1_odelimstr3
booger1_o/4
booger1_odelimstr4
booger1_o/5
booger1_odelimstr5
booger1_o/6
booger1_odelimstr6
booger1_o/7
booger1_odelimstr7
booger1_o/8
booger1_odelimstr8
booger1_o/9
booger1_odelimstr9
--Return--
/home/mbenjamin/dev/rgw/s3_py/python/boto3_delim.py(48)<module>()->None
-> import pdb; pdb.set_trace()
(Pdb) res1['Contents']
[{u'LastModified': datetime.datetime(2019, 1, 22, 14, 18, 49, 986000, tzinfo=tzutc()), u'ETag': '"fae5a6cd8860a054e995074ebbdfed96"', u'StorageClass': 'STANDARD', u'Key': u'booger1_odelimstr0', u'Owner': {u'DisplayName': 'M. Tester', u'ID': 'testid'}, u'Size': 27}, {u'LastModified': datetime.datetime(2019, 1, 22, 14, 18, 50, 10000, tzinfo=tzutc()), u'ETag': '"42ebe1ea120446769900301adc024fbd"', u'StorageClass': 'STANDARD', u'Key': u'booger1_odelimstr1', u'Owner': {u'DisplayName': 'M. Tester', u'ID': 'testid'}, u'Size': 27}, {u'LastModified': datetime.datetime(2019, 1, 22, 14, 18, 50, 33000, tzinfo=tzutc()), u'ETag': '"239b00602a834b95b969cff88b2f3a0b"', u'StorageClass': 'STANDARD', u'Key': u'booger1_odelimstr2', u'Owner': {u'DisplayName': 'M. Tester', u'ID': 'testid'}, u'Size': 27}, {u'LastModified': datetime.datetime(2019, 1, 22, 14, 18, 50, 57000, tzinfo=tzutc()), u'ETag': '"674c10103d7897b8cb432bbee25a337b"', u'StorageClass': 'STANDARD', u'Key': u'booger1_odelimstr3', u'Owner': {u'DisplayName': 'M. Tester', u'ID': 'testid'}, u'Size': 27}, {u'LastModified': datetime.datetime(2019, 1, 22, 14, 18, 50, 82000, tzinfo=tzutc()), u'ETag': '"928f354462bac7f8c54165d3ff54abf8"', u'StorageClass': 'STANDARD', u'Key': u'booger1_odelimstr4', u'Owner': {u'DisplayName': 'M. Tester', u'ID': 'testid'}, u'Size': 27}, {u'LastModified': datetime.datetime(2019, 1, 22, 14, 18, 50, 110000, tzinfo=tzutc()), u'ETag': '"f0337c3c6f8748bb22cd9082bcdcf141"', u'StorageClass': 'STANDARD', u'Key': u'booger1_odelimstr5', u'Owner': {u'DisplayName': 'M. Tester', u'ID': 'testid'}, u'Size': 27}, {u'LastModified': datetime.datetime(2019, 1, 22, 14, 18, 50, 139000, tzinfo=tzutc()), u'ETag': '"61887c860aa8b01d66c2b003c22ac8c1"', u'StorageClass': 'STANDARD', u'Key': u'booger1_odelimstr6', u'Owner': {u'DisplayName': 'M. Tester', u'ID': 'testid'}, u'Size': 27}, {u'LastModified': datetime.datetime(2019, 1, 22, 14, 18, 50, 164000, tzinfo=tzutc()), u'ETag': '"5bd2c5172b0fa130afcf462500c1c2a8"', u'StorageClass'
: 'STANDARD', u'Key': u'booger1_odelimstr7', u'Owner': {u'DisplayName': 'M. Tester', u'ID': 'testid'}, u'Size': 27}, {u'LastModified': datetime.datetime(2019, 1, 22, 14, 18, 50, 190000, tzinfo=tzutc()), u'ETag': '"04c6b5752e9ee1e398b26a77f07aface"', u'StorageClass': 'STANDARD', u'Key': u'booger1_odelimstr8', u'Owner': {u'DisplayName': 'M. Tester', u'ID': 'testid'}, u'Size': 27}, {u'LastModified': datetime.datetime(2019, 1, 22, 14, 18, 50, 214000, tzinfo=tzutc()), u'ETag': '"bba67116d7f4d851ec87b0ff4c78fad8"', u'StorageClass': 'STANDARD', u'Key': u'booger1_odelimstr9', u'Owner': {u'DisplayName': 'M. Tester', u'ID': 'testid'}, u'Size': 27}]
(Pdb) res2['Contents']
[{u'LastModified': datetime.datetime(2019, 1, 22, 14, 18, 49, 972000, tzinfo=tzutc()), u'ETag': '"3f8b20cbb1f737642aac6bf8c60a7292"', u'StorageClass': 'STANDARD', u'Key': u'booger1_o/0', u'Owner': {u'DisplayName': 'M. Tester', u'ID': 'testid'}, u'Size': 20}, {u'LastModified': datetime.datetime(2019, 1, 22, 14, 18, 49, 998000, tzinfo=tzutc()), u'ETag': '"4ffaac0b975094d602e20d8bef0d5d21"', u'StorageClass': 'STANDARD', u'Key': u'booger1_o/1', u'Owner': {u'DisplayName': 'M. Tester', u'ID': 'testid'}, u'Size': 20}, {u'LastModified': datetime.datetime(2019, 1, 22, 14, 18, 50, 21000, tzinfo=tzutc()), u'ETag': '"92ddaf02b0976ba3bcf468d8c8fa1058"', u'StorageClass': 'STANDARD', u'Key': u'booger1_o/2', u'Owner': {u'DisplayName': 'M. Tester', u'ID': 'testid'}, u'Size': 20}, {u'LastModified': datetime.datetime(2019, 1, 22, 14, 18, 50, 47000, tzinfo=tzutc()), u'ETag': '"02b711bf2813232e913e9ee8e325dc84"', u'StorageClass': 'STANDARD', u'Key': u'booger1_o/3', u'Owner': {u'DisplayName': 'M. Tester', u'ID': 'testid'}, u'Size': 20}, {u'LastModified': datetime.datetime(2019, 1, 22, 14, 18, 50, 69000, tzinfo=tzutc()), u'ETag': '"65ae618e5ebf4230ceb5a1920627bbfe"', u'StorageClass': 'STANDARD', u'Key': u'booger1_o/4', u'Owner': {u'DisplayName': 'M. Tester', u'ID': 'testid'}, u'Size': 20}, {u'LastModified': datetime.datetime(2019, 1, 22, 14, 18, 50, 96000, tzinfo=tzutc()), u'ETag': '"33b93c887b04c3055d43f697b2198551"', u'StorageClass': 'STANDARD', u'Key': u'booger1_o/5', u'Owner': {u'DisplayName': 'M. Tester', u'ID': 'testid'}, u'Size': 20}, {u'LastModified': datetime.datetime(2019, 1, 22, 14, 18, 50, 124000, tzinfo=tzutc()), u'ETag': '"d8513f670a3f9284ee351575c3be8a48"', u'StorageClass': 'STANDARD', u'Key': u'booger1_o/6', u'Owner': {u'DisplayName': 'M. Tester', u'ID': 'testid'}, u'Size': 20}, {u'LastModified': datetime.datetime(2019, 1, 22, 14, 18, 50, 151000, tzinfo=tzutc()), u'ETag': '"02dbf66f6e9f56ac8d3d162cdf6dc97f"', u'StorageClass': 'STANDARD', u'Key': u'booger1_o/7', u'Owner': {
u'DisplayName': 'M. Tester', u'ID': 'testid'}, u'Size': 20}, {u'LastModified': datetime.datetime(2019, 1, 22, 14, 18, 50, 177000, tzinfo=tzutc()), u'ETag': '"63fa5214e65428f57591d1a964e6d91c"', u'StorageClass': 'STANDARD', u'Key': u'booger1_o/8', u'Owner': {u'DisplayName': 'M. Tester', u'ID': 'testid'}, u'Size': 20}, {u'LastModified': datetime.datetime(2019, 1, 22, 14, 18, 50, 202000, tzinfo=tzutc()), u'ETag': '"9b694e3829d1d99ee83adc61a0ecccb7"', u'StorageClass': 'STANDARD', u'Key': u'booger1_o/9', u'Owner': {u'DisplayName': 'M. Tester', u'ID': 'testid'}, u'Size': 20}]
(Pdb) res2['Contents']0
{u'LastModified': datetime.datetime(2019, 1, 22, 14, 18, 49, 972000, tzinfo=tzutc()), u'ETag': '"3f8b20cbb1f737642aac6bf8c60a7292"', u'StorageClass': 'STANDARD', u'Key': u'booger1_o/0', u'Owner': {u'DisplayName': 'M. Tester', u'ID': 'testid'}, u'Size': 20}
(Pdb) res2['Contents']1
{u'LastModified': datetime.datetime(2019, 1, 22, 14, 18, 49, 998000, tzinfo=tzutc()), u'ETag': '"4ffaac0b975094d602e20d8bef0d5d21"', u'StorageClass': 'STANDARD', u'Key': u'booger1_o/1', u'Owner': {u'DisplayName': 'M. Tester', u'ID': 'testid'}, u'Size': 20}
(Pdb) res2['Contents']2
{u'LastModified': datetime.datetime(2019, 1, 22, 14, 18, 50, 21000, tzinfo=tzutc()), u'ETag': '"92ddaf02b0976ba3bcf468d8c8fa1058"', u'StorageClass': 'STANDARD', u'Key': u'booger1_o/2', u'Owner': {u'DisplayName': 'M. Tester', u'ID': 'testid'}, u'Size': 20}
(Pdb) res1['Contents']0
{u'LastModified': datetime.datetime(2019, 1, 22, 14, 18, 49, 986000, tzinfo=tzutc()), u'ETag': '"fae5a6cd8860a054e995074ebbdfed96"', u'StorageClass': 'STANDARD', u'Key': u'booger1_odelimstr0', u'Owner': {u'DisplayName': 'M. Tester', u'ID': 'testid'}, u'Size': 27}
(Pdb) res1['Contents']1
{u'LastModified': datetime.datetime(2019, 1, 22, 14, 18, 50, 10000, tzinfo=tzutc()), u'ETag': '"42ebe1ea120446769900301adc024fbd"', u'StorageClass': 'STANDARD', u'Key': u'booger1_odelimstr1', u'Owner': {u'DisplayName': 'M. Tester', u'ID': 'testid'}, u'Size': 27}
(Pdb) res1['Contents']2
{u'LastModified': datetime.datetime(2019, 1, 22, 14, 18, 50, 33000, tzinfo=tzutc()), u'ETag': '"239b00602a834b95b969cff88b2f3a0b"', u'StorageClass': 'STANDARD', u'Key': u'booger1_odelimstr2', u'Owner': {u'DisplayName': 'M. Tester', u'ID': 'testid'}, u'Size': 27}
(Pdb)