There's a bug in the current version that causes a crash any time you try to return to an encounter that you had fed a berry to before fleeing. Can happen with wild pokemon too, but is particularly bad if you berry'd queued reward encounters.

They also announced they're going to cap the reward queue at 100, but due to the bug they extended the deadline to clear out any extras (to like the end of August I think? But double-check if you have a ton).