Cubase 11 Pro - Sound issue & UI freeze when closing Halion SE VST plugin window

I have a project with a single VST instrument, Halion Sonic SE 3.

Inside Halion I loaded the 16 channels with Iconica Sections & Players presets. All Halion outputs are mapped to tracks in Cubase. Max preload is set to 6400Mb in Halion.

I created a MIDI track for each of those channels too.

All of this goes through a Steinberg UR22C in USB 3 mode, 44.1kHz. That’s about the setup.

Windows 11, Dell XPS 15 9500, 32Gb, i7 8 cores, SSD

When I play fast using my MIDI keyboard (ie when a lot of samples are playing at the same time), audio starts to distort, crackle and eventually drops.

I tried different latency modes & buffer lengths but to no avail. The audio performance meter is really high, even in Stable mode at 512 samples.

The real bummer is, when I try to close the Halion window, Cubase freezes and I need to end it via task manager. Audio continues to work . I can play notes on the MIDI controller and it works. But everything is frozen.

LatencyMon reports no issues.

Anyone in here can help me?