I am able to reproduce this issue on a test server. It looks like this is due to a change somewhere in the EL8 build of Apache 2.4.62, which was actually released with 7.13.48 last week (as that is the first version I can reproduce with. I cannot reproduce on a CentOS 7 server with the same version).
I’m submitting a bug report, but I don’t have an ETA at this time. In the short-term, please use domain.com:2443/webmail, instead.
Thanks for letting us know!
Thanks,
Jenna
Friendly Neighborhood InterWorx Support Manager