Invoke-SPOSiteSwap Issues

MarkusBundschuhDHBW 

I had the same issue, contacted MSFT Support, but they did not have any solution available. I went and solved it myself. Apparently for large organisations (10000+ seats) you'll have to use the page diagnostic tool which works for Edge and Chrome. I don't  understand how this plugin communicates its findings back to Powershell, but apparently it does. Although I solved all the errors the diagnostic tool showed me the first few times I kept getting the same error in PS. What I did was the following:

1) Created a blank page on the classic teamsite (current root) and promoted that to Start Page

2) Created a blank page on the Communication Site (new to be root) and promoted that to Start Page

3) Reran the Page Diagnostic Tool on both site collection homepages (both old an new)

4) Relaunched my PowerShell session and executed the command (with -force and -nowait parameters)

5) Worked!

For some reason the new or old web parts on homepages block the siteswap from happening, but nobody knows what exactly goes wrong. Hope this helps.