After a recent update, alle custom fields data on my trello cards is missing

[admin]

After a recent update, alle custom fields data on my trello cards is missing (fields stil exist but valuesare empty) This happend across multiple cards. I need to know if this dat can be restored from backup or logs, or is our whole date from the previous version gone?  Can I get the data back of our clients? 

[Oleksandr]

Hi!

To check if your data is permanently deleted or just not displaying in the UI, you can use the JSON trick on a specific card.

1. Open a card where the custom field data is missing.
2. Add ".json" to the end of the card's URL in your browser address bar and press Enter.
3. Search the page (Ctrl+F or Cmd+F) for "customFieldItems".

If your values appear there, the data is still in the database and this is a display bug. If the array is empty, the data is actually gone. For data restoration from backups or logs, you must contact Trello Support directly at https://trello.com/contact, as standard users do not have access to backend restoration tools.

For the future, to automatically track changes to custom fields, you can install the Board Assistant Power-Up: https://trello.com/power-ups/685016dd47b5654ae385bba6
It tracks custom field modifications and records them as comments on the card on behalf of the user who made the changes, creating a reliable log of all actions.