Thanks for the comment. I've managed to find most photos on Google photos, so I haven't completely lost out.
It's just strange that thousands of photos can disappear from multiple gallery folders, not even appearing in the deleted folder. Most were taken with my phone camera and where in the gallery album "camera".
There's a few other threads on here with similar issues after the recent software download.
A reminder for everyone to cloud backup photos, or print the important ones.
Thanks again for your time.
N