Photos app stuck on "closing the library"

Hello,

I have been uploading a large photo library to iCloud for the las two weeks.

I let it run for a few hours each day and sometimes overnight.

This afternoon I noticed that progress bar and the number of photos had not changed since last night so I thought I should start the app.

I selected Pause. Sometimes it takes a few minute. to stop but nothing happened for an hour. So I quit the app. It has been stuck on "closing the library" for over four hours.

I searched community and google and some people with this problem let it run, others say it goes for days with no end, some force quit with no problems while others find it corrupts the library.

What should I do? Is four hours enough or should I let it go overnight and see what happens?