I know this is an old post, but still wanted to add my additional comments, for others like me that came looking for a solution.

I have had this issue of seemingly randomly expanding regions and non-regioned Subs/Functions for YEARS now...

Unfortunately, to this day, there still is NO solution or fix.

It happens randomly when Pasting/Cutting/Deleting code lines/blocks, which causes Visual Studio to re-evaluate the entire code, "solving problems" with how the code is displayed, thus resulting in the collapsed code blocks expanding.

I have just created another Microsoft Developer Community Issue Report about this issue. I hope this time Microsoft will take it more seriously, because it is really impacting my ability to finish projects....

Here is the link to the issue report: https://developercommunity.visualstudio.com/t/Collapsed-regions-keep-randomly-expandin/10821359