Are your videos being removed or being hidden (private)? When videos get removed, you will lose views from those videos.
If not, it could be YT doing cleaning up of bots & spam accounts that are manipulating views.
Any accounts using "illicit services" to artificially spike their subscribers and watch hours will get a spanking by YT. I am not saying that you are but I have seen these "services" being pedaled. I keep getting spammed by one company called MyFollowers. I am not sure how they got my email address. I constantly delete them. I have zero interest in such BS "services".