LMS : This site can't provide a secure connection

I had to change my LAN & wifi router. Everything seems to be ok and all my Squeezebox players including Squeezelite on the PC work correctly. When I try and browse my LMS I get this error on all devices (Windows 10 and 11 and Android tablet and phone):

This site can’t provide a secure connection
192.168.1.10 sent an invalid response.
Try running Windows Network Diagnostics.
ERR_SSL_PROTOCOL_ERROR

Windows Network Diagnostics can find no problem.

I can't see anything in the router setup that would affect the PCs but allow the Squeezeboxes to function correctly. I did not change LMS in any way.

Help please!
Thanks.