WiFi speeds dropping out and then restarting – Ethernet connection fine

[#1]

Hi all, new plusnet customer. Fibre broadband on ethernet is fine, but most devices have trouble connecting to the wifi and speeds fluctuate wildly, from 10-20 kbps to 50-60 mbps. I'm using the plusnet router, i changed the name of my router to one that I've always used, could this be a factor?

[#2]

No, more likely to be interference from other users on the same channels, and not having separate 2.4 and 5Ghz channels , there are plenty of advice on how to check and change on here.