Elegoo Neptune 4 plus, suddenly all prints failed

[Lez0]

I've been using my new Neptune 4 plus without any problems for months now.
All of a sudden I'm getting a blob of plastic instead of my print.
I'd watch it start OK then it would prick up the print and start dancing around with it.
I had my prints failing after checking all sorts of things, different filaments, levelling etc.
At one time I had to strip the head as it was covered in a big blob of plastic.
Factory reset didn't help.
After searching the web I found a youtube video saying the firmware needed to be updated as the printer wasn't saving the z height.
Firmware updated OK.
I then set about levelling the printer. I reset it many times saving the settings, switching off/on and trying again before I was happy.
I wanted to be 100% I would get a good print.
The test Buddha printed perfectly, what a relief.
Still like the printer.

Lez