Fibre connection up and down

[#1]

For several weeks my fibre connection has been up and down. Originally thought it might have been the plusnet provided router to blame. Got a loan of a known good netgear router and thought things were sorted. But my family have been moaning thats its not sorted anything and the connection is still up and down. Today was pretty bad and my usual remedy of bouncing the router and/or bt openreach modem didn't help. Called plusnet and they said they can't detect any issue. Got to wait up to 4 days for a response (feels slow).
Given i've swapped the router i'm thinking it might be the modem but wanted to see if anyone has experienced issues with a bt openreach modem before?

[#2]

Hi Yoko83,

Have you been able to test connecting a device directly to the router with an ethernet cable? I ask as that would help eliminite perhaps an issue with the WiFi signal dropping or perhaps being affected by interference.