I finally found the solution (dumb me). I have a property in my character base class named ‘initial walk speed’ which would be set when the character is spawned. This value was equal server-client. The problem was that this property would set the max walk speed on spawn which was NOT properly replicated, thus resulting in a movement speed difference between server and client.
Thanks for your detailed explanation, this surely did help a lot with ruling out probabilities! @Rev0verDrive