Some of them are downvoted and that is fine. The problem is that most of my comments (lately almost all of them) are not visible at all.
Could it be that I am classified as “dumb” by some automated spam protection?
"you" are not classified as dumb, there is a demotion of content that is not being consumed, until it goes stale and falls off the "end".
also comments that are downvoted heavily enough are greyed then removed from view.
I do not think that is the case. The last time I commented I logged out immediately after posting it, and when I am logged out, the comment is not visible. I see it when I’m logged in.
that is a "shadow" i dont know why anybody thinks its a good thing, but what happens is you see your posts and comments, but no one else does, so you think everything is fine, instead of abandoning the username and making another.
Ive wondered just how much storage space is "wasted" by perpetuating the illusion of participation when you are actually talking to thin air.
Which would imply that the solution might (if downvotes are the issue) be to consider how the content of your comments might be viewed by others and then try to adjust your commenting style so as to not be downvoted by others.