WAU3604 8GB is soldered and 32GB are socketted in, so they are mismatched. And I have had consistent black screen crashes on both Windows and Linux if I go above 8GB
Memory mismatching shouldn't be a problem per se. Just today I installed an expansion 32 GB DIMM module into my Thinkpad T14 with a Ryzen 7 PRO 4750U which originally had a soldered-in 16 GB memory chip(s).
No problems whatsoever so far. Maybe it won't reach the top possible speed because of the single/dual channel matching stuff, but I don't care. I need to volume to avoid even thinking about needing to enable any swap.
You may want to run memtest86+ to see if your expansion DIMM module is all right.