I've tried using mono adapters, they don't seem to work at all.

So far, the only thing that's worked for me - and this is going from the X850B 5 years ago to new X850G / X950G models this year - is not pushing the cable in all the way. Judging by not having any issues using this with the X850B over those 5 years, the connection will be fine.

Back when I discovered this issue with the X850B, I suggested for others that if they were concerned they could try to find some plastic/nylon washers they could install on the cable end to use as spacers.