There is some very strange behavior occuring with protocol handlers and taskpane addins from newer office versions.
I've done extensive testing and found that if I have a protocol url such as "ms-excel:nft|u|https://office.iwriter365.com/api/getFile/test.xltx" This protocol works perfectly fine until the moment I start a taskpane with the taskpane url "https://office.iwriter365.com". After this Excel will display the error "Microsoft Excel can not access the file...." every time I launch the protocol url.
The only way to make the protocol url function again is by closing all instances of Excel.
This has started happening somewhere around Office version 1802 or 1803.
