Without access to a library that replicates the problem, the only other option is to wait until I have time to add extensive logging so that users can generate log files for me that I can investigate. If either of you wants to share two .msb files (one for each device) that exhibits the problem, I can certainly look into it using that, otherwise it may be a while, because, like I said, I don't see the issue even with libraries that are several gigabytes in size. I should also mention that, if you use your own storage location for MobileSheets, this may slow down file I/O due to how Microsoft handles file permissions with UWP applications. I'm able to implement some optimizations if the default storage location is used to speed up certain file operations, but these optimizations don't work if users choose their own folder to manage things. There is nothing that can be done about that until I switch the Windows version of MobileSheets to a different framework (which is something I am considering either later this year or next year).
Mike
Mike