Hey there, thanks for taking the time to register and posting a bug a bug report! I'll need to know what version of the game you're playing on, and if possible the save file where you couldn't launch the dropship on the mission anymore. I've tried testing it out a bit on my end and unfortunately I haven't been able to reproduce the bug on my end, so getting a save file with the reproducible bug would be a godsend.
I'll link a guide below to help you find where your saves are, thanks a lot!