I'm also experiencing this as of today. Strangely, I had no issues with the multithread exe before today, load times were much faster than single threaded. But today even opening the mission editor is 10-15 minutes. I've removed all mods, tried a repair, I've cleared fxo/shaders, I just can't understand how it worked fine for days and then literally overnight it borked itself.
Edit 1 - I've attached a log file showing a 4-5 minute load time just when trying to create a new mission in the mission editor.
Edit 2 - The old DCS.exe in the normal bin folder has normal load time performance. Opening a mission in mission editor is less than 30 seconds.
dcs.log