We have the following Items:
mysql.slavestatus[Last_SQL_Error]
which returns text of SQL Error
Also we have:
web.page.regexp[localhost,"/monitor.html",8080,"Overall status: (WARNING|OK|ERROR)",]
which returns "Overall status: OK" or "Overall status: ERROR" or "Overall status: WARNING"
We have few more items with text/character "Type of information" but it doesn't matter since issue happens with all of them.

For items above we have the following triggers:

{Template App MySQL:mysql.slavestatus[Last_SQL_Error].strlen(0)}

>0

{Template App Sync:web.page.regexp[localhost,"/monitor.html",8080,"Overall status: (WARNING|OK|ERROR)",].str(OK)}

#1

The problem is if trigger becomes PROBLEM, Zabbix sends alerts with PROBLEM at each check, i.e. each 30 seconds, while trigger is active.

This happens with any type of text function, like str, diff, strlen, regexp, etc.