"Create board from template" on a large template (1000+ open cards) gets the UI stuck on Creating Board but succeeds in the background

Issue Summary

"Create board from template" on a large template (1000+ open cards) gets the UI stuck on Creating Board but succeeds in the background. This is reproducible on our end on this board https://trello.com/b/n4frJO2t# which identified the UI bug - it has a lot of open cards and stickers: https://trfind.prod.atl-paas.net/board/639dde3b8ddc5504bd407b51 .

Steps to Reproduce

1. Open a large template such as https://trello.com/b/n4frJO2t#
2. Click on Create board from template and enter the information for the destination board.

Expected Results

Destination board gets created and the message Creating board completes.

Actual Results

The message Creating Boards comes up but remains there indefinitely, the web response is returning a 504 (Gateway Timeout) however the actual action of copying the board does occur in the background.

Workaround

Reducing the number of artefacts on the template board (cards and/or stickers) would mitigate the issue but we don't know the threshold at which the action completes successfully in the UI.