Subtasks suddenly marked as not completed in batch after restart

[Gert-dev]

Describe the bug
Today when I started Planify, I suddenly got a bunch (10 or so) of 'overdue' tasks that have already been completed a few months ago, around August and September mostly. I did not do so manually and nothing else in the database reverted or went corrupt.

All the tasks in question were subtasks of the same parent task. I've had this occur once before and this was also the case then.

To Reproduce
I'm not sure exactly what triggered this, but I can explain what I did:

1. Have a parent task with a bunch of subtasks.
2. Mark most as completed.
3. Restart Planify (at some point in the future).
4. The tasks have been marked as undone.

Expected behavior
Subtasks that are done don't get marked as undone.

Desktop (please complete the following information):

• OS or DE: [e.g. pantheon, unity, gnome]: GNOME 47
• Version [e.g. 0.1.2]: 4.11.6

Additional context
Investigating the database, I see that all these subtasks in the Items table have had the completed_at field set back to empty, and checked is also now marked as 0. I still have a backup of my database from last week and they are all marked correctly with completed_at filled in and checked set to 1 there.