We have had a large drop in views, but it wasn't necessarily just in March. September is always a killer for us when kids go back to school and watch less video, and this year was worse than normal. Things usually turn around in October, but then things fizzled out again just before Halloween.
I have reason to believe that YouTube has changed what counts as a "view" sometime around mid-October. At that point, our views definitely decreased but our watch time INCREASED dramatically (like 30-40 seconds per video). So to me I think YouTube is re-defining what counts as a view. That's just my own anectdotal stats, though.
Mostly overall though I think we're facing a lot more competition than when we started years ago. It used to be that there were no imitators, now there are tons of them, and often their videos will do much better than our own.
As an older channel too, I think viewers may be fatigued by all these new videos and can't be expected to keep up them all. We have over a million subs, but our last month of newly uploaded videos averaged about 67,000 views per video, far from a million. Most of our views don't come from subs anyway, so we rely on the "Suggested videos" algorithm to do the job for us, but the competition there is fierce. Our back catalog brings us most of our views, some of our oldest videos are still top 5 view getters per month.
I wonder how they are calculating it differently?? I'd have thought that a minute watched is a minute watched... Maybe they are rounding up now? o.0