Reconnection problems

I have a problem that looks like the one described in https://community.ring.com/conversations/ring-alarm/ring-stopped-working-applied-all-known-troubleshooting-will-get-stuck-on-95-and-then-error-and-will-not-connect-to-wifi-help-please/666b1bf98795e77fa3a2f045?lang=en  - I try to connect my doorbell and it gets to 95% and then gets stuck and then times out. However in my router's interface I can see that it does actually connect and gets an IP address via DHCP during that "stuck" phase. I have tried the things suggested int he fix for that, but none of them have had any impact. The only difference is that I have gone from a cable internet modem (Virgin Media in the UK) to a 4G LTE router (TP-Link TL-MR6400). That router only supports 2.4G, but everything else is perfectly happy to connect to it. There is something about the wireless setup of it that the ring doorbell and the cameras don't like. Any thoughts what it could be given that they *do* establish a connection. I have other cameras that I am not trying to re-setup, and from time to time they show up as having got a DHCP-ed address as well.