We have a trigger action with an Update/Recovery operation set to "Notify all involved", with "Default media type" set to a specific type (e.g. MS Teams) rather than "All".

Any user who leaves a comment/update on the problem is treated as "involved", even if they have no media of the type configured for the action. Zabbix still attempts to notify them via that specific media type, and the attempt fails.

Affects versions: 7.4.2

Steps to reproduce:

1. User A has MS Teams media configured. User B has only Email configured (no MS Teams media at all).
2. Create an action with an Update operation: "Notify all involved" enabled, "Default media type" = MS Teams.
3. Trigger a problem; the initial notification goes to User A via MS Teams as expected.
4. User B adds a comment/update to the problem.
5. The problem updates again (another comment, or it's resolved).

Expected result: User B is skipped for this operation, since they have no MS Teams media — nothing to send.

Actual result: Reports → Action log shows a failed alert for User B with error "No media defined for user.", even though User B has Email configured — Zabbix is trying to reach them through a media type they never set up, instead of just skipping them.

Additional info: There's no way to work around this without disabling "Notify all involved".