We just dropped Plusnet.
Plusnet are good, it’s just they don’t have amazing routers in terms of WiFi signal, although it’s hard to blame that when there are so many other issues with house layout, location of router, walls, neighbours, other interfering devices.
I’d have just got a good Wireless Access Point and turn off the WiFi in the router. No need to change ISP.
Anyway, as for the original problem, does the issue happen when far from the router or in another room with a brick wall between you and router?
I’ve noticed latest Android phones getting really fussy on low signal strength. Still enough signal but they decide they can’t do anything yet a laptop can. Similar with mobile signal. 4G and good signal, fine. Poor signal and struggles. Happy with slow but it just thinks it can’t do anything. Drops to 3G or E, and no data at all which is daft as we used to live with non 4G for years and have data. Not fast sure, but at least it will load a web page. Now it just sits there like there’s no signal at all.
P.s. Those with 5ghz issues. 5ghz has a shorter range. It’s okay if you’re close to the router and had advantage of probably less interference, but 2.4ghz still cover the house better. Still though in some cases you’ll need additional access points.