@the ducks
I had in searchbox tags:false when it crashed.
did not press next or previous on more than 50 books which were all modified.
Did not manage tags or authors or anything.
I started calibre typed tags:false in searchbar and was happily downloading data one book at a time when it crashed.
I restarted it found the modified column and clicked on it.
Not the end of the world or even upsetting, perhaps disconcerting. I can just convert all 907 books and carry on

or find the majority of changed books etc.
Just wonder what I could have done.
Calibre usually only crashes when I have typed something stupid in the book conversion search and replace which I haven't done today (so far

)
Helen