Accidently click on a different DOFF section on the menu. Tried to go back the collect reward option no longer there... Has anyone else had this bug?
If you mean the box that pops up with Lt. Ferra saying you have reached a new tier and can choose a new tier-appropriate DOff, yes, it's not a 'bug' as such, but if you open another window like the exchange or inventory menu, it 'replaces' that commendation window (they're apparently the same type of window and you can only have one open at a time).
No problems tho, just go to Starfleet Academy, talk to Lt Ferra and visit the store (or if you're on the Klingon side, whatever the equivalent is there). Your commendation token and list of DOffs will be there so you can collect them.