Here is something interesting from Youtube help page
>How engagement metrics are counted>Change in metrics>After legitimate engagement events are counted, your metric count should update more often.>The timing of these changes varies depending on a video or channel's popularity and views.>Keep in mind that we're constantly confirming and adjusting engagement events.>On some videos and channels, your metric count might seem frozen or not show the metrics that you expect.>Metrics are algorithmically confirmed to maintain fair and positive experiences for content creators, advertisers, and viewers.>To verify that metrics are accurate, YouTube may temporarily slow down, freeze, or change your metric count, and discard low-quality playbacks.>Note: Using several devices to watch the same video and streaming the same video across several windows and tabs are examples of low-quality playbacks.What caught my attention was this sentence
>On some videos and channels, your metric count might seem frozen or not show the metrics that you expect.This more or less confirm they apply different freezes and verification for different channels and videos
https://support.google.com/youtube/answer/2991785 