I get probably 5-20 line dropouts per day. It can happen at any time and under any circumstances.
The Plusnet router stopped working so it's been replaced with an Asus VSDL router which has a lot more control over everything. The settings are all set up to run 'stable' (rather than for maximum speed), but still the dropouts persist.
I think there may be a fault with the line. I had PN fibre at our old address any only get very occasional dropouts. At this address it's an order of magnitude worse!
I don't have a telephone to check the 'sound' of the line (line is used for broadband only).