Have there been changes to making/uploading custom models? I noticed that the ones I use are not being affected by the stats.
yes, it now supports all versions of VRM models not just v1.0 and you can tie stats to any body sliders on the model, not just the old defaults. the models you're using probably don't have the any sliders. you need to get a model that already has them or create the sliders in blender. the NSFW Character Model has the old default body sliders and is fully compatible if you want to simply use that.