Our Internet keeps dropping after fibre was installed

[ABAC]

We've had fibre installed a few weeks ago and since then our Internet drops several times a day. We have to restart the router every day - despite Sky giving us a new one.

The BT openreach has 2 solid lights and a third that keeps flashing green. When we run tests it shows good speed which is why Sky won't help, claiming all is well. We are at a loss! We both work from home and keep being thrown out of meetings!