Investigating rollbacks in Postgres
I wouldn't expect the mere presence of a rollback to be a problem.  There are all kinds of reasons this might happen and nearly all are harmless.  A good rule of thumb is that if the application requested a roll back, it is harmless at least for the DBA...

The key is to log statements in errors (which would force rollbacks) and investigate those.  The other possibility which is possibly concerning is in serialization failures (if using serializable transactions) but here the application has the responsibility of handling the rollback.