There are two known issue for HTML Access running on Edge browser through UAG, see VMware Horizon HTML Access 4.9 Release Notes
Copied as below:
If you use a self-signed certificate with Unified Access Gateway, you might not be able to access a Horizon desktop when you use a Microsoft Edge Web browser for your HTML Access session.
Workaround: Use one of the following workarounds to resolve this issue.
- Use a valid CA-signed certificate.
- Do not use port 8443 for the Blast External URL property. Use port 443 instead.
or this one:
If you configured Unified Access Gateway with a root certificate that is signed by a Certificate Authority (CA) and the Blast External URL property value is set to blank or to port 8443, you might not be able to connect to a Horizon desktop if you are using a Microsoft Edge browser. Once the error happens, all new connected sessions are not visible.
Workaround: Use one of the following workarounds to resolve the issue.
- Set the Blast External URL property to port 443.
- Close the Micrrosoft Edge browser, then relaunch the HTML Access Web Client and connect to a desktop.