Using sentry_sdk version 0.13.0 in Python 3.7.3, strings encoded as bytes objects are serialized as lists of integers:

>>> from sentry_sdk.serializer import serialize
>>> serialize(b'123abc')
[49, 50, 51, 97, 98, 99]
>>> serialize(b'123abc', should_repr_strings=True)
['49', '50', '51', '97', '98', '99']

This doesn't seem like the expected behavior, instead it could be:

>>> serialize(b'123abc')
'123abc'
>>> serialize(b'123abc', should_repr_strings=True)
"b'123abc'"

I was able to reproduce the issue with Python 3.7.3, 3.6.7, 3.5.6 and 3.4.10. The serialization seems to behave properly with Python 2.7.