Hello,
You’re right, that tutorial doesn’t apply to your issue.
If you were just adding cards to your local/personal decks and suddenly, with no apparent reason, all the Front fields changed to blank, that’s a rare bug. Everything suggests this is an Anki error, not something caused by AnkiHub.
If the issue happened recently (which seems to be the case), you can restore a backup made before the problem occurred. This will bring your collection back to how it was at that time, with minimal loss of progress.
Please follow this tutorial:
How to Restore from Backup
This bug likely won’t happen again, and restoring the backup should fix the issue.
However, if it does happen again, please let me know!
You can also post about it on the official Anki forum to see if anyone has insight into what might have caused it:
https://forums.ankiweb.net/