MacOS - Excel - Copy / paste causes spinning beachball

I'm looking for suggestions as to the cause / solution to a spinning beachball every time I try and copy/paste in Excel. This happens more on some spreadsheets, but is happening in one I use frequently which is only 700 KB. I am using **Office 365**, and my MBP (Mac Book Pro) is 2018 (2.6 GHz i7, 32 GB RAM), running Catalina. It does however seem independent of device, as I recreated it on my partners MacBook Air (2011, 2.0 GHz i7, 8 GB RAM) running High Sierra. The desired file is stored locally but mirrored in iCloud). I am aware that was a problem in Office 2011 for Mac, but my online search hasn't found posts with this problem recently. I have tried an older suggested workaround of copy/pasting a blank cell in a blank spreadsheet before opening the desired file as suggested at https://apple.stackexchange.com/questions/249326/excel-2011-copy-and-paste-beachball-hang-freeze-issue I have also tested with desired file mirrored on a different cloud, and also just saved locally without any cloud mirroring, - all have similar problems. Thanks @pion for the specific detailed advice to capture what my system is doing when it happens. This is available on Github, spindump.txt .