Hi, I am an add-on developer. I submitted an add-on several days ago, it has been reviewed and thus not signed, but public to users. When trying to install it, I got an error message:
It can be installed after review.
So the add-on is not incompatible, corrupt, or conflict with others.
I guess it’s because of the add-on ID. After being reviewed, the add-on is signed with a permanent add-on ID. But before that, the unreviewed version has no add-on ID, which cannot be installed as mentioned here.