This is continuation of a ZBX-9660 discussion.

We've discussed it a bit now and agreed that would be much more user friendly to not allow store incorrect expression as discussed in ZBX-9660.
Otherwise people will face with such case all the time and will be disappointed when figured out that it's an absolutely not obvious limitation.

Sasha confirmed that the expression considered to be incorrect (as for server) only for "AND with several Triggers".

We could add such sanity check on frontend side and do not allow to store incorrect expression.