Update, I seem to have solved it.
After adding the EditAnywhere tag to my components, I could see the variables in the instance placed in the level. Apparently, one of the components was set to None, which caused the crash.
It is important to note that I was using the Hot-Reload compilator, and reading online, it seems that it could sometimes cause some problems with the connection with the blueprints. I had to recreate a completely fresh Blueprint (not duplicating my existing one) inherited from my class and the variable seemed to be fine when placing the newly created Blueprint.
I never started using Live Coding because it didn’t seem to work when reloading with it, but now it seems that I have to find out how it works because it seems like a more safer way to compile my project.