Hello Tobbe,

The DriveShaft and its extension bars have a form-fitted connection. Having the screws „Hand tight“ is more than enough for a solid, straight connection that stays in place.
It could be the case that the screws got tightened too much. - This does not harm the screws or thread but the screws can push through and simply "bend" the metal plate that sits between the extension bars and the middle piece to prevent marks and scratches from the screws. As a quick fix, you could remove the metal plates and apply some oil (any bicycle chain oil will do the job but please avoid WD-40) onto the extension bars. For anything else, please write me an email and I should be able to hook you up with some spares.

Best regards
Dennis