I'm trying to import a text backup from 8.3 into 8.4, but it is failing about a third of the way into the import. I enabled debug-detailed verbosity, and the last errors to appear are:

2018-03-22 17:03:39 (1) failed to find typ commentstring during import, position 620373221
2018-03-22 17:03:39 (1) failed to find typ Timed Backup at 01:00, 22/03/2018 during import, position 620373257

What does this mean exactly, and how do I fix it?

There are also other messages appearing during the import, such as:

2018-03-22 16:57:52 (-1) failed to import a record of type RLinkVc pos 325909343
and
2018-03-22 17:03:25 (-1) failed to find typ 60 during import, position 593887278

but these are not stopping the import. I imagine the (1) is a more serious problem than the (-1).