I've had the same problem in the past, for me it seems to be fixed. I can switch branches while viewing a source code file.
Amber Van Heckestaff
Thanks for confirming that this problem is fixed for you Moritz, I am going to change this ticket to closed. Clemens if you continue to have issues please reach out to https://support.atlassian.com/contact/#/ and mention me directly, so we can figure out what is going on.