I had a similar event not so long ago.
I was on my 3rd solo flight, all was going well; was circuit bashing until ATC requested i'd depart the circuit for some heavy traffic inbound/outbound and other Heli movements. Anyway, all was fine on my rejoin, clearance to continue, 1 ahead, notify ATC of final but no response. After a quick check i was not transmitting (the little icon was not showing) failed and failed again, about to climb and change transponder when my final attempt worked, clearance confirmed all within good time, landed and returned to my dispersal. All this lasted about 20-30 seconds if that.
Good learning for me since i had only completed around 16 hours total; good confidence boost when things don't go quite exactly as planned. (first time out the circuit on my own too!)