Thank you @Ralph77 - this exclusion from the SP settings works! When I got in there, I realised that I had excluded Excel last year when I had problems with it; I had forgotten about that.
I am grateful for your work - I would not have thought of this kind of problem. As I have over 14500 notes, lots of tags and links, I thought it would be me. I have indexed, rebuilt, optimised etc, but all to no avail - yet I didn't have the problem on my work computer. Now I understand why!!
Again, thanks for your help and for posting the fix.