I have a 2018 iPad Pro and Cubsasis 3.3.1 is so unstable for me, I can’t even use it anymore.
This should not be the case.
Do you own the USB-C iPad model?
Here, several owners of this device reported about problems with several music apps in the following Audiobus forum thread.
In addition, please give the following steps a try, to see if it helps to immediately resolve your issues:
(1) Set “Audio Engine Latency” to “OFF”
(2) Load an empty project
(3) Close all running apps, including Cubasis
(4) Fully shut down the iPad
Please keep me updated about your results!