Hey! Thanks for the answer. There was no offset anywhere to be found, and I also tried this with a new character BP, as well as the original Unreal mannequin - same results. 
I then updated my game version from 5.1 to 5.1.1, the issue remained.
However, I found that in a new project this error did not happen, so what I ended up doing was merging a clean Character BP from that new project file to my old one, and literally readding every piece of code in there as well as in a new Anim BP. Took quite a lot of time but in the end it worked. It seemed legit like a bug as I have tried everything, and I mean absolutely everything to remedy this, only for it to work flawlessly in another project.
I believe this error might have come about because I started my project in UE5 beta version, and updated it along with new engine releases. I noticed, that the character BP from my UE5 build had some minor differences in the details panel, compared to the UE5.1.1 one. (Mainly I could see the character mesh’s Translation and Rotation in my version, where as the UE5.1.1 one had only Scale visible there) That was the only reason why I think it might have been an engine upgrade thing, and turns out it was!