Custom log event definition has "Allow merge" checked. At same time 3 various log messages are generated and catched by mentioned custom log event's Log query. Problem generated by this custom log event contains ONLY last (top one, when looking into log via Dynatrace Log GUI) of 3 messages. Is this an expected behaviour of "Merge" action ?
In this case 3 lines we treated as different were in fact the same. 😉 Combination of specific log entry properties constructs uniqueness of event (i cannot remember exactly which ones actually). One common detection rule was used originally, solution for this issue was to detect specific log entries in separate detection rules.