I have a basemodel (this slugcat) that I can export to cpmmodel just fine on CPM 0.6.11a for 1.12.2, but fails due to size limitations (model data overflow) on CPM 0.6.17b for 1.20.1. The exported model from the 1.12 install functions without issue on my 1.20.1 client & server, which suggests it's just something getting miscalculated or being overzealous in the file size limiter.