If not already using a Cat7 or Cat8 cable; upgrade to that while inspecting the other connections for damage to the sheath. Check the connector collet for looseness or broken pin. The only loose part of it should be the nut. Before you screw it back on also check the connector on the modem. It should be clean and tight.
Log into the user interface of your modem and navigate to its utilities section and look at the error log and contact your ISP about them.