Weird Wifi problem Pi Zero W

I have a Pi Zero W with a weird Wifi issue.
The Pi runs an SSH gateway and is powered from a USB port on the router. It's been running faultlessly for about 2years now with a few tweaks to the standard setup to mount regularly written to files on a ramdisk to preserve the SDcard. The system reboots every 24hrs as a simple way of stopping the ramdisk  filling up.
After a new router was installed, this Pi has issues connecting to Wifi.
Power it up and there's a 75% chance it will connect. If it doesn't removing and reapplying power makes it likely to connect. If you reboot it from the command line it fails to connect most times.
I have a spare Pi Zero W and swapped the SDcard into the spare. Connects every time on reboot or on power-cycle. I place another SDcard in the intermittent one and the same Wifi connection problem exists. One card is Debian 12 with NetworkManager and one is Debian 11 with old style networking setup.
The fault moves with the Pi and doesn't seem to be software dependent. Using Debian 12 and checking with a USB Ethernet connection the Wifi fails with "could not activate connection: Activation failed: secrets were required but not provided" even though the password is set and has connected. I've checked there's no dust/dirt or other contamination on the PCB. I've powered it from several different USB ports (desktop, router, phone charger).  The rest of the Pi seems to work fine when the Ethernet connection is in use. Or when it was in an original Pi Model A with a USB Wifi dongle, it boots and the Wifi connects. The software image appears OK. It's just this Pi Zero W with iffy Wifi.
Has anyone seen anything like this? Most annoying. Any ideas?