Have you tried MixFix? It's a patch that allows loading loose LUA files amongst other things for SRTTR.EDIT: After a lot of testing, it seems like the bug is being caused by the Misc Lua Patch which is cited as a requirement for Sandbox+. Removing it seems to solve the issue although you'd have to give up Sandbox+ as well.
Have you tried MixFix? It's a patch that allows loading loose LUA files amongst other things for SRTTR.
It seems to be the more stable option for me (although installing DXVK alongside ASI loader was a headache).
So basically using vanilla misc.vpp_pc