Hello,
This happens because AnkiHub overwrites your fields when updates are available for the deck. To make and keep changes to a specific field, you need to protect it.
Since this is a very important field and is likely to receive frequent updates, the best approach is to protect it only on the specific cards you have edited. You can do this by right-clicking the card, choosing the “Protect Fields” option, selecting the field you want to protect, and then clicking OK:
If you’ve already made many edits and it’s too much work to fix them manually, you can restore your collection from a backup (How to Restore from Backup). Once you’ve restored it, protect the field on your edited cards, and it won’t be overwritten again.
Note: When you protect a field, you will no longer receive any updates for that field.
Let me know if this solves your issue! 