You'll need to get the transmission computer (EGS) codes read to find out what's going on. Your normal bluetooth/WiFi to phone type scanner will not do the job as it only talks to the engine computer (DME).
Find someone local with INPA set up on a computer or set it up on your own windows computer with it. Link to INPA below
https://www.bimmerforums.com/forum/showthread.php?2184573-The-Z3-Diagnostics-Thread-Instructions-Experiences-Discussions-Experimentation
Alternatively, its off to the BMW dealer or independant service center that knows about BMW's.