I've done this - which solved the issue. I'm a typical non-tech person and applied the easiest solution, which I think this is.
I hope Plesk will update the KB once they're done with the fix, and to guide what actions to take based on the various "work-arounds" that have been applied.
It worked for me too! Although it appears to be a different solution from: Website suddenly started to show 500 error: AH10292: Invalid proxy UDS filename.
Hope this wouldn't give any long term issues!