1) Why are these conversion exceptions occurring, when as far as I can tell, the response data is always correct?
You expected data that looks like this:
{"foo":"bar"}But Gson found something more like:
Hello!It was expecting a JSON object beginning (aka the { character) but it found a string-like character instead.
2) Does retrofit do any sort of caching for GET requests? This might explain why re-requesting a failed request continues to fail until I kill and restart the application.
Retrofit has no caching whatsoever.
Depending on what HTTP client you are using, it may cache the response of a GET request depending on the headers. Usually you have to opt-in to cache behavior in an HTTP client so if you haven't done that, I doubt it's enabled.