OWA “Manage Add-ins” Stuck Loading After Clicking Settings (Exchange 2019 CU15 / Exchange SE RTM)

I have an Exchange Server environment with three versions: Exchange Server 2019 CU14 Dec25SU, Exchange Server 2019 CU15 Sept25H, Exchange Server SE RTM, and Exchange Server SE RTM Dec25SU.

Issue: When users click the Settings icon/button in OWA/Outlook on the web and then click Manage add-ins, the page does not redirect and remains stuck on an external loading screen.

Tested environments:

Exchange Server 2019 CU14 Dec25SU: Works without issues

Exchange Server 2019 CU15 Sept25H, Exchange Server SE RTM, and Exchange Server SE RTM Dec25SU: Does not work on any of them

Troubleshooting performed:

Moved all arbitral mailboxes to a database on Exchange Server SE RTM Dec25SU (the most recent version in the forest). (No success)

Migrated all servers to Exchange Server SE RTM Dec25SU. (No success)

Isolated testing using the hosts file (DNS) pointing to each host individually, and all hosts have the issue.

All SE RTM Dec25SU servers were installed in admin mode via Command Prompt. I also ran the two .ps1 scripts below on a test host after installing the SU:

#learn.microsoft.com/en-us/troubleshoot/exchange/client-connectivity/owa-stops-working-after-update

cd "C:\Program Files\Microsoft\Exchange Server\V15\Bin"

.\UpdateCas.ps1

.\UpdateConfigFiles.ps1

iisreset /restart

Workaround: With the user already authenticated, if I manually open the URL below in the same authenticated session, it loads normally:

webapp.mydomain.com/owa/#path=/options/manageapps

Does anyone know how to fix this, or if this is a bug that started with CU15 (or a later SU)?