This morning I was playing with a toy app I have which uses Retrofit, and I’ve found the following problem with it (and Instant Run):
02-16 07:41:55.550 2976-2976/com.test.android A/art: art/runtime/thread.cc:1329] Throwing new exception 'length=227; index=1017' with unexpected pending exception: java.lang.ArrayIndexOutOfBoundsException: length=227; index=1017
The exception was in the call itself, so it was either Retrofit doing strange things or something deeper. I found the problem to be because of some interaction between ART and Instant Run, and it was already reported.
All in all, currently there is no fully reliable solution. So, if you find this problem in a call using Retrofit, the best course of action is to disable Instant Run and rebuild. Preferences -> Build, Execution, Deployment -> Instant Run -> (uncheck) Enable Instant Run to hot swap code/resource changes on deploy (default enabled)