vanilla Zabbix, MySQL db, linux (oel 6)

Related issue ZBXNEXT-551.
Current issue description does not contain all details, I mean that action disabled automatically too, as it should (documented in ZBX-7948).

Key point here is custom expression.
I can reproduce it on frontend 2.4.7rc1.
Simpler custom expression to reproduce is "A and B and C" where one of them is template/host or probably any other entity type, documented in https://www.zabbix.com/documentation/2.4/manual/config/notifications/action/conditions#actions_disabled_due_to_deleted_objects.

Even if you have custom expression with two members only "A and B", then deleting one of them leaves the custom expression unmodified in database (actions.formula) but it's not visible in frontend because with single condition, "Type of calculation" settings are not displayed at all and it's even worse.

Hard to decide how it could be improved for custom expressions.
If fix expression automatically- which and|or to remove? before or after removed reference (if both exists)?
It could be possible, when and|or are before or after reference only. Or when C reference has identical "and" or "or" on both sides, like "... and C and ..." or "... or C or ..."
But if for example we remove D from "... and D or ...", what should be removed with D "and" or "or"? Good question ....

If not fixed in code - then have to be additionally documented, definitely.

Server side was not tested.

CONFIRMED.

Prohibiting removal of templates used in custom expressions would put the burden on the admin and protect the system.

I think things can be solved / prevented here by:

• As mentioned above by preventing objects being deleted that are involved with actions
• Do not allow the enabling of actions via the actions list status toggle that have invalid custom expressions or as I experienced many events actions were invoked.