I have had my struggles with icons, but I think I have overcome all the pitfalls now.
One thing I discovered though is that sometimes when adding a dynamic icon, it will show up immediately and sometimes it just needs a bit of time. I guess maybe there is an old one still in a cache somewhere.
Anyway, if you have really checked everything and can’t see any mistakes, either wait, or give your icon a different name. (the filename(s) as well as the name.)
That usually solves the few issues I sometimes have with icons. That and the odd typo every once and a while