Ahh yes, apperantly there is a bug going around nowadays about grounded planes preventing an army to move.
The problem here is that tanks have little damage value againts planes and vice versa. Planes use their full stat line even on ground like there "flying".
Because of the morale and HP of both plane and tank is still high and both have little attack value againts one another they will be stuck on limbo till the end of time.
I suggest to bring Anti-Air guns or interceptors to remedy this to save your tanks, while the bug is being worked by the devs.