Yes, e.g. for DCI with ID 291 there are consecutive SYS_THRESHOLD_REACHED events without SYS_THRESHOLD_REARMED in between.
Can you show output of the following on your database:
select * from event_cfg where event_name like '%REARM%';
select * from thresholds where item_id = 291;
Can you show output of the following on your database:
select * from event_cfg where event_name like '%REARM%';
select * from thresholds where item_id = 291;