Does the noise margin vary? And if so when and by how much? You could be getting moisture onto the joints if they are not sealed which might cause some problems although if they cannot track to earth or each other it will be less.
Get a copy of RouterStatsLight and leave it running for 48 hours to monitor the line and see what happens. But before that try the following.
Turn off power to the hub and wait 1 minute.
Disconnect the lead from socket to hub.
Leave everything OFF for an hour - yes, ISPs say three to five minutes, however from experience a longer period can help.
Power-up the hub and allow it to fully settle - say 5 minutes.
Reconnect the lead from hub to socket
Wait for 2 or three minutes
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