Issue connecting to externally initiated MS Teams Meetings

We use Office 365 and we are heavy MS Teams users at our company.  We have no issues with internal meetings with other members of the company, however we often have issues 'joining' externally created Teams meetings initiated by our customers or vendors who are also using Office 365.   The issue seems to be with the desktop client...when we try to join the interface will say 'connecting' but just seems to hang there...never connects.  We then fall back and have to use the web interface from the office.com portal.  We can connect using that.  What would cause this issue, only with external meetings, from our desktop interface?  I can also say that it does not seem to be a problem 100% of the time... I know of some users who do not experience this problem and can connect from the desktop interface to an external meeting, but I also know of many of our users (8-10) who have reported this issue of just hanging on 'connecting'.   Thanks!