SYNC Timing Synchronization failure - Loss of Sync

For the past 4 weeks I’ve had constant broadband issues where the connection drops for a couple of minutes. Every occurrence of this coincides with the following critical error being logged in the modem: SYNC Timing Synchronization failure - Loss of Sync.

An engineer came out last week to have a look and stated that “the signals are too high” so they reduced the signals. Unfortunately this has not fixed the issue.

I’ve also noticed that when the internet drops it often coincides with the TV picture breaking up briefly.

Anyone got any advice on how to move forward?