Over the last couple days I have done 8 or 9 random FPs, and despite joining randomly and completing all objectives, no completion crates. Sent in a ticket, Bioware's response...'Tough luck, file a bug report have a good day'. So I guess I'll be playing ESO since I can't complete end game content. It's always something with MMO's

I had this same problem. After research it, I learned that, when this is happening, you have an active instance of a FP that you have not cleared. You can tell by looking at the FP filters in GF. There are supposed to be 23 vet FPs and 25 Master FPs showing in the filters.

 

If you have a FP stuck in this state, you will see only 22 vet and 24 mm. if so, look at your FP list and try to figure out which FP is missing. For me it was Crisis on Umbara, which was gone from my checklist.

 

To fix this I traveled to the FP entrance, stepped inside, then exited. That cleared the error. My FP totals on my GF filters went back up to 23 vet and 25 mm, and I could start receiving daily reward boxes again.