Hi Developer_75,
In my experience, it is normal.
In general, when you join a meeting with Lync web app, it is supposed to ask you to join as a guest or use credentials. Using credentials can provide a better experience.
Perhaps, you need to check if you have published simple URL meet to the Internet successfully, including the DNS records and the SAN entries of the certificate on Reverse Proxy as
the following pictures.


Best Regards,
Sharon Zhao
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