Helix Rack as playback device with Qlab via USB: audio pops and clicks?

[mmtmusic]

Scenario: Qlab is running tracks, video and Helix patch/snapshot changes. Whereas we used to run Qlab thru a dedicated audio interface for larger shows and only MIDI commands being sent to the Rack, for smaller venues we assumed that the Rack could be used as an interface itself. Guitar paths are 1a to 2b to XLR only, whilst mono click is being sent to USB 7 and to the Send 3 out and stereo track is USB 3/4 sent to the 1/4" outs. Global EQ is only on the XLR outs. FX Loop 1 is being used for an 1176 style comp but that's entirely analogue so obviously no potential cause of issue.

The only USB audio channels assigned in Qlab are USB 7 and 3/4. 

The issue we're getting is random pops and clicks on the playback. Qlab is on an M2 Pro MacBook (and not reporting any playback errors in its logs) so we can only assume its the Helix struggling to manage both tasks: an amp sim and a 3-channel playback device. Qlab is always running audio at 48kHz and using the standard Core Audio driver.
 

We're aware that there will always be a brief silence on the audio outs whilst switching patches during playback and we can just about work/live with that by having simply not doing it. But have we hit a wall in the Rack's processing power? Can it not handle what we're asking of it?