This occurs in large Qt projects in visual studio.

Steps to reproduce:

1. Open VS 2017 (15.5.7)
2. Open a solution (.sln) which includes a Qt project, with subclasses using the Q_OBJECT macro.
3. Modify the source file of one of these classes.
4. Save the file
5. (Visual studio hangs for 15-20 seconds)
6. File is saved

Something the addin is doing is computationally expensive as the hang is not present when the addin is disabled.

(Feel free to write to me if you need any more details)