I'm not sure what more to say than that. Any of the tickets where I was a member, I am still a member, but the previous memebership otherwise has been wiped out. The card history still shows that those people were added to the cards at one point, but no longer. Is there a way to fix this without manually going into dozens of cards and reassigning members?
When moving cards across boards, any members that are not on both boards are removed from the cards (because of access permissions). You need to make sure the members are added to the destination board before the move.
Regarding fixing it, adding one or more members to multiple cards can be done with third party automation tools. But if the members are different for each card, then you'll need to use the API to write a program to recover the members and re-add them. I can give you guidance if you want to go down that route.
To recover the members from cards already copied, you will need to first find the source card. You can obtain this by issuing this API request:
Where CARD_ID is the id of a copied card.
This will return an array of actions, which should only contain one object. This object will have a data field with a cardSource object in it.
Take the id field from the cardSource object and use it to read the members from the source card: