O365 SharePoint - I can not change to Modern Experience for Library

[Chris_Gillespie]

I have a document library that I was using both Classic Experience and Modern Experience.  I would have to switch to Classic Experience to paste in several columns of data.  Now the library will not switch back to Modern Experience.  I have gone into Advanced Settings and set to Modern Experience many times, but it never takes.

[#2]

@Chris_Gillespie First try in incognito mode and see if the change is happening and if possible try in one of the other browser.

Then make sure there is no other web part added on the page

Finally check whether this behavior is only for this document library or for all and check in other site collection as well.