I see YouTubers claim that YT does this, but personally, I've never encountered a single video on a channel that I'm subscribed to that didn't show up in my subscriptions feed. I've also never seen direct evidence, it's only YouTubers claiming that this is happening to their subscribers, as a way of explaining some downturn in the number of views. I suspect many of them are confused about the "notification" feature, which I don't know I've ever seen anyone actually use. (Also, sometimes a video can get stuck in "processing", in which case it won't show up in the feed until it's finished processing.)

Do you have some examples of this happening? I'm almost certain if you could provide screenshots, e.g. of the channel and of your subscription feed, showing the missing video, that YouTube would consider this a bug. The subscription feed is supposed to show all the new videos from channels you're subscribed to.