I never use F11 (had to check what it does - Restart), my go to key is F5, so I thought I would follow Pendrush's steps:
1. Yep, large project
2. Yep
3. Pressed F11
And got the following in the IDE log.
Gui: 946
System.Exception: Error compiling program.
Error description: An item with the same key has already been added.
Error occurred on line: 39
End Sub
at cy.a(List`1 A_0, String A_1)
at a7.b()
at ed.a(Object A_0)
Compilation task: 2980.3499
Gui: 112
Compilation task: 5555.157
which is slightly different to what I had seen before. At step 3, I didn't do Ctrl+S, just F11, so I am guessing the IDE saved the changes automatically before restarting, hence the Ctrl+S isn't required.
As before, compiling again, straight after receiving the error, everything is back to normal and the project compiles without error.