After upgrade to 10.1.21, triggers (maybe not all) stopped working, downgrading to 10.1.20 fixed the problem. Attaching table and trigger definition, here is SQL command:
insert into outbox (`UDH`,`SendingDateTime`,`DestinationNumber`,`TextDecoded`,`MultiPart`,`SenderID`) values ('','','0900123123','test','false','');
The result is that NOTHING is inserted into table and no errors or warnings are reported. Maybe it's related to
MDEV-11698 (the only thing related to triggers in 10.1.21 changelog)?