Kaniken’s post suggests that the problem is connected to Defender and/or the AV program in use. ST’s indexer scans all the project files to build its database for symbol lookup so that you can jump to func definition etc… It seems to work on several threads to achieve its ends quickly and works with most languages. Perhaps a good workaround is to configure the AV/Defender to skip any files requested for opening by sublime.exe. How you do this will depend on your AV, and I’m not sure with Defender; I use neither.
It may be that either or Defender 8.1 is blocking sublime more vicously than Defender 7 or