My iCloud storage is suddenly full, Messages storage jumped 8 GB in minutes. Is this an iOS 15 bug?

I am pretty aggressive about managing my iCloud storage to stay within the 50 GB plan, so I am constantly checking my storage and deleting what I do not need. At one moment I was at approx. 42 GB worth of storage and when I picked my phone up minutes later I got the dreaded notification telling me my iCloud storage was almost full and I should upgrade to 200 GB. When I checked it appears that my Messages in iCloud has magically jumped from 11 GB to a whopping 20 GB. Nothing changed. No one sent me 9 GB worth of messages, photos, video, etc.—it came out of nowhere.

Is this a bug that Apple is aware of in iOS 15? Specifically I am on iOS 15.1.1.