Issue with large Boards

Server Setup Information:

• Did you test in newest Wekan?: YES
• Wekan version: v5.65
• Operating System: Debian Linux
• Deployment Method: docker
• Http frontend if any: Apache
• Node Version: 12.22.7
• MongoDB Version: 3.2.21
• What webbrowser version are you using? FF 91.2.0esr and Chrome 94.0.4606.81

Problem description:

• Broswers (latest FF oder Chrome) got really slow with such a huge board. All Cards have Checklists (copied from a template card)
  An export JSON is 60MB, including an orphan pdf attachement. I sedded the attachments out (sed -e 's/"file":".*=="//g') and got an 22MB JSON.
  Importing this in an empty localhost Docker wekan works, but still got seconds of Click-Delays. Importing in the Production Server wont work. Chrome is not able to parse the JSON after pasting it and Firefox offered the User-Mapping screen but stops working after clicking on Finish.
• The Board has Rules to move Cards to the next Collumn when a Checkbox is checked.
• Browsers RAM Usage is over 4GB when entering the Board.
• It's hanging only with Admin Users.
• Can send you the JSON Export to reproduce
• In webbrowser Consoles says nothing
• No Docker Logs