This may be a cable problem or a RJ45 problem.
Good work have nice day.so the cable was the culprit.
i installed 3 different Mikrotik devices at the tower end of the cable and was facing the same problem and that made me zoom in on the problem.
the cable length is 65 meters.
change the cable finally!!!
Yes of course grounding is very importantthe link was working for 2 years in the current setup and suddenly this happened. do you think grounding would do this issue?link grounding?