Cannot login to EmonCMS at all

I have been running EmonCMS 10.2.2 for several years in a shared hosting environment. It has worked perfectly.
Today (5 Feb 2023) I cannot login at all. I receive no error, the system just returns to the login screen. I have tried from Firefox, where I have had a page permanently open on the Feeds screen, and likewise from Chrome on Android, where again I have had a permanently open screen.

I have been sending JSON light data via GET for several years but this broke a few days ago and has possibly been sending garbage while I resolve the problem.

I have looked at the database and from the outside it looks OK, the API key and username is correct (obviously I cannot confirm the password is OK).

How can I get logged in again? Any guidance will be very welcome. I am quite familiar with php and MySQL so am happy to dig a little if required.

Thanks in advance

My guess is your host has forced an update of the underlying PHP? I doubt V10 will run on even the most recent supported PHP as V10 is way behind (and we did have things that had to change as PHP changed).

You may find that manually running the install scripts might work, not sure how you installed in the first place.

Is the backup module installed? You may be able to run the backup manually and imort to a fresh instance.

It largely depends what you installed and how it is running. Did you use REDIS for instance?

Can you view the Apache logs?