This has been reported for some time, and nothing appears to be being done about it.
I just ran into the same issue.
And if the only solution is the use chrome, I probably just lost a customer. After about 60 hours of work. Customer still running win7 w/ IE11.
MS does not support updates to Win7 services, so some O365 services seem to be less friendly to support on WIN7/IE.
It is also happening on my Win10 device, with Edge or IE11. Same exact thing, reduce to 80% an it works. Multple resolutions on the screens. Further more IE11 is still on the supported list, so they are suppose to work. Support needs to get this fixed.
Screenshot in Edge