The tickets no longer match the filter query for the board, such as if they indicate they need to be in a certain status (of if that status in not mapped to the columns), or with a specific field setting.
You can figure out why by taking the filter query and confirming the ticket appears if you just do a regular search with those parameters. If it does not appear, then the board won't ever see it. If it does appear, you should check the sub-filter, quick filters, and status mapping to see if it's not-visible for those reasons.
A common solution for scrum boards is to confirm that the ticket is in the open sprint on that board.
You must be a registered user to add a comment. If you've already registered, sign in. Otherwise, register and sign in.