Web Add-ins missing in OWA

Hi,

I've noticed that when installing custom Add-ins from a manifest file or the AppStore, they don't appear in Outlook on the Web (OWA) immediately. It can take anywhere from 1 to 6 hours before they become visible.

I've ruled out browser cache issues.

When checking with PowerShell connected to Exchange Online, the Add-ins show as Enabled = True

Get-App -Mailbox ***@***.onmicrosoft.com | Select-Object DisplayName, AppId, Enabled

This issue occurs both in our production tenant and sandbox  tenant, and seems to happen randomly.

For example, when accessing apps directly from https://outlook.office365.com/mail/inclientstore://outlook.office365.com/mail/inclientstore, the Script Lab add-in doesn't show up. I also installed the Zoom add-in from its manifest URL (https://zoom.us/office365/add-in/manifest.xml://zoom.us/office365/add-in/manifest.xml), but it doesn't appear immediately either.

These are user-installed add-ins, not deployed centrally.

Do you have any insights into what might be causing this delay and how it can be mitigated?

Thank you in advance.