Mariadb/MyISAM: Incompatible key or row definition between the MariaDB .frm file and the information in the storage engine. You have to dump an

We have a db with around 150 tables in, of which about 30 or so are partitioned as such :

ALTER TABLE `myTable`
  REORGANIZE PARTITION PFUTURE INTO (PARTITION P201910 VALUES LESS THAN ('2019-11-01'),
             PARTITION PFUTURE VALUES LESS THAN MAXVALUE);

We’ve been automatically partitioning these tables on a monthly basis for around 3 years now without any issue. Recently on 1 of the tables, after a partitioning exercise (with no errors/warnings reported) we see this :

Got error 190 “Incompatible key or row definition between the MariaDB
.frm file and the information in the storage engine. You have to dump
an

from storage engine MyISAM” whilst running a show table status. I have restored from a backup (after stopping/starting mariadb) and re-issued the command, and the same error is reported.

Repair table fails with the same message.

Is there a process I can follow to un-corrupt the table and make the partitioning process complete?

We’re using MariaDB 10.4.8. We are not in a position to use any other table format, MyISAM is what we have and what we have to stick with for now.

What I should mention is that we recently upgraded to MariaDB 10.4.8, and although I’d instantly jump on that as being the cause, the other 29 tables partitioned perfectly.