That sounds like an issue with Misstortion2, not with vst3shell. Does Misstortion2 work in any other VST host, both loaded directly or through vst3shell?

I can confirm Misstortion2 2.3.0 (the version I'm trying to get into OpenMPT) works on my desktop with FL Studio.
I haven't tried loading Misstortion2 with vst3shell on another program because I don't have any other programs or know of any other programs that would require vst3shell to run vst3 plugins.

You can still try using vst3shell with FL Studio or Renoise or some other VST2-compatible host to see if it works through vst3shell in that host, even if they also support VST3 plugins. That way I was able to confirm that Misstortion2 works for me both through vst3shell in Renoise and OpenMPT, as well as natively as a VST3 plugin in Renoise.

I installed vst3shell on my desktop and followed the same steps I did on my laptop with OpenMPT, and was able to get Misstortion2 working just fine with vst3shell on my desktop.
I don't have or know of any other software that I could try testing vst3shell on my laptop, the only software I have a license to is ACID Pro 5.0, and FL Studio 2024, both installed on my desktop.
If you need me to test something on my laptop that I've done on my desktop I'll be willing to try it here.

All of this points to either vst3shell or Misstortion2 being the culprit; I'm afraid you have to ask their respective authors for help.

Dang it, I was hoping my problem would be easier to fix than I thought, thanks for the help though.
I have an idea of where to contact the developers of Misstortion2 but I don't know where I could contact the devs of vst3shell.

The KVR thread is the right place to ask. polac is the developer of vst3shell.