First I know that custom fields are a premium feature and one of my companies pays for that. I have two accounts for two companies and often use Company 2's account as it is my "main" account but it is on the free plan only.
I was customizing a board created by someone at Company 1 (paid plan) using a lot of custom fields. I realized it was viewable to the entire workspace when it should not be. I created a new workspace and moved the board to the new workspace. My custom fields all disappeared and Trello now says to upgrade to add custom fields.
I may have moved it using Company 2's free account, but why would it let me do that? So it seems I created a new workspace on my free account and that deleted the custom fields and several hours of work with no warning. Is there a way to undo this?
I figured this out, but the Admin of the board had to restart to be able to move the board back. Their option to move the board was not in the menu anymore. After restart it was there. they were able to move the board back and the custom fields reappeared.