Why does Calc fail to respond for so long when I activate it?

I switched from using Excel because it kept having a fatal error when I tried to save my files. Libre Office Calc doesn’t have that problem but it’s terribly slow whenever I want to switch to it from another application. It says “Not Responding” for up to five minutes or so. In the meantime I’ve often opened Excel instead, done what I needed to do, and closed it again.

What’s causing this and is there anything I can do about it?

Thanks.

Please try resetting the user profile. https://wiki.documentfoundation.org/UserProfile

this slowness is very frustrating, have 3spreadsheets open and all three hung for half an hour. what do i do except press X in the top right corner, then i try and open one spread sheet again, and a window come up for recovery of 3 spreadsheets… takes time… all three spreadsheets recover, but i still cannot close either of them. ???