Can't copy paste clips wavelab pro 8.5

This has just started happening trying to paste clips in montage and getting worse as it zips me out of montage window into audio window. This used to be instant. I’m wondering if it’s cache and temporary files as I’ve never cleared them for years as I don’t know where they are. Or can it be space on c drive. This started happening overnight. When it started it didn’t zip me out of montage window into audio window, it stayed in montage window, now it’s zipping me out. When I go back in clips have pasted but twenty seconds later. I can’t select all the clips and go copy by right clicking then paste as it only copy’s one clip so need to do the drag and drop by having curser show the square thing on top of clip. Sorry I just can’t explain it and video will not upload and I can’t reduce size of video.

Edit checked for errors on drive and space I have 64gb on c drive and 5 tb on g drive which is where all my files and montages are.

What version of windows are you using? You might want to check is your windows (user account etc.) is working fine as I am able to copy paste in WL8.