We continue to have hit or miss on Externals invited as Presenters.
Teams client appears to hang when Externals have Teams for other organization Teams.
Also had two Externals added with their hospital email addresses...
Could not get them in. They gave us their personal Microsoft accounts ......we added them.... and that worked 1st try !!!
Our business units are getting frustrated and also point to how easy Zoom is and Google Hangouts..
We created a test account and ensured that it could connect. We then at times share that account with Externals.. then change the PWD when meeting is over.