How to recover missing iCloud Drive files after upgrading storage plan?

Quite of few files disapeared from my iCloud Drive. I recently upgraded from the Apple One Family plan to the Apple One Premier plan which change my iCloud+ plan from 200GB to 2TB of storage. Wondering if this may have triggered something to cause this and if Apple could magically make the missing files appear again. Has anyone run across this problem before?

[Re-Titled by Moderator]

Original Title: Missing iCloud files?