Smart Controls window in GarageBand "freezes"

I am running GarageBand 10.3.4 in Catalina 10.15.

Every time I introduce a software instrument or guitar amp emulation the Smart Control window "freezes". I can still use it, but the knobs don't turn. For example, if I turn up the reverb, I can hear the reverb coming up, but the window is "frozen" so the knobs don't show where it is set. Also as an example it doesn't show the controls for the instrument or amp, when I change to that type of track, but is frozen in the blue "compressor, EQ and sends" window.

This only happens when I create one of the before mentioned types of tracks. If there are only audio tracks in the session, the problem does not occur.

I have never had this problem before, but it happened when I installed Catalina. It isn't a periodic problem either, happens every time.

Thanks in advance!