Laggy interface

Hi everyone,

I have a serious issue with Cubase 10.5 which terribly slows down my work. I have just upgraded to version 11 but the issue is still there.

I have a project with a lot of MIDI tracks connected to virtual instruments.
Whenever I move the playhead or press the play/stop button, the interface freezes for several seconds before effectively moving the playhead or playing/stopping the playback. During this time I can’t do anything and if I try moving the playhead during playback, the music freezes for several seconds before starting at the new location (loosing in the mean time a lot of measures).
During the freeze I see that all of my tracks MIDI activity indicator also freeze.
I tried attaching a MIDI monitor to a track and I noticed that it send all of the MIDI data every time I move the playhead. Since my project consists of nearly one hundred of MIDI tracks, could it be that this can cause the slow down?
All of my MIDI tracks make use of expression map and I noticed that the freeze occurs even when the virtual instruments are not connected with the tracks.

Here is my hardware:
• iMac 27" 2020
• RAM: 128GB
• CPU: i9 3.6GHz 10-core
• SSD: internal 4TB NVMe

I tried reaching out at Cubase support. We had a TeamViewer remote session where they told me they would give me resolution info at the end of the week when they would have talk to the developers… 45 days have passed and nobody replied me (even after subsequent enquiries).

Hope you can help.
Thanks in advance