Visual Studio errors since using perforce

Hey guys,

first I have to admit that I am relatively new to this topic.
For a university project, I started learning Unreal Engine 4 development with C++. I set up a perforce server to collaborate with my teammates. I am the only C++ developer, so, the code is only relevant to me.
As a workflow, when I start working I just check out the whole source directory, but my cpp files behave strangely. They just don’t seem to get any reference to the header files. Here an example of how horrible bloody red the classes look like:

The header files are definitely readable since I checked out the whole source directory!
Interestingly, I can perform intelli-sense operations from the header file into the cpp file, but not vice versa. Restarting the editor hasn’t saved me.
Deleting the .vs directory, regenerating the visual studio solution hasn’t worked out either.

I really appreciate your help and time in advance
Thank you!