For troubleshooting sake it's always best to use known good hardware. That said, swap out one piece at a time. So eliminate one cable with another completely different, unused cable and see if the problem persists. If issue persists, move on to the next possible cause of the issue.
Pro tip* take a clean, dry, toothbrush and gently clean the gold contacts on the male ends of the ethernet cable. If visually dirty upon inspection after dry scrubbing, lightly dab toothbrush bristles in isopropyl alcohol and again, gently scrub each rj45 male end a couple times. Set aside for a few minutes until dry. Do not insert back into a LAN port whilst wet.
Ethernet cables do not last forever. If the clip that holds it into the socket is broken, replace it. If there are any visual kinks in the cable sheath, replace it. They are not expensive. I would suggest purchasing category six (cat6 gigabit) or higher.
If you are noticing connectivity issues aside from aforementioned tips and able to visualize connecting Network Equipment, verify they are not powering down, as that is also a common issue. Power supplies fail quite often. It doesn't matter if it is a cheap $100 home router or a $20,000+ network appliance. Plugged power supplies run 24/7 and simply fail sometimes sooner than later. It is not uncommon for a power supply to shut down and turn itself back on. I hope that helps. Be well