I downloaded a challenge from a user called Vahilior and ran into an annoying bug: A group of his fighters suddenly flew off into the bottom right hand corner and either got stuck there or flew off the map - I could still see their names but my units couldn’t target them. My bombers did the same shortly after, either in pursuit (although I had deleted fighter attack order for them) or just following the same pattern. This caused half of my fleet to ignore targets next to them and chase after that group (despite priorities set for cruisers/frigates) therefore flying around the corner in question leaving one cruiser at mercy of enemy ships. I haven’t been able to check the challenge again, but it almost cost me my victory; you can only imagine what happens when long-range frigates with little to no shield protection fly next to enemy cruisers. 
I’ll try that challenge again tomorrow and see what happens, I’m not going to be able to do that just now. Has anybody else experienced that?