The above issue occurred last night so I just tested Cubasis 2 VER 3.8.3 right now and it still does not work. I get the same issue as above. Only playback and no input audio coming from my guitar through the Apogee Jam Plus. Might be a Cubasis issue because the following iPad apps below worked with no problem.
Garageband, Amplitude, BiasFX, JamUp Pro and Xdrummer all worked for playback and recording with the Apogee Jam Plus using the Apogee USB C cable plugged directly from Jam Plus to iPad Pro 2020 11” running iPadOS Ver 13.4.1