There are a few things to note here:
1. Data for milestones in-app (this includes on mobile) usually updates every couple of hours but... for
some data it gets pulled from statfire and not youtube api.
2. Video views and metrics can be delayed in their updates by up to 24-48hours when being pulled from statfire site.
3. Video views will go down if a video is unlisted privateded so that could also cause number to go down.
4. From what I am seeing being reported in statfire for your channel, it seems to be inline with what TubeBuddy is matching →
https://statfire.com/channels/UCbT6bph6TcR-6ByiXzU3RYg
Hope that helps