I ran into this because of an error on my side.

I added a new block type called "Contact block" with the machine name "contact_block". Something went wrong with my connection, and the form didnt refresh. I created another bean with the same name "Contact block" but different machine name "contact_block_information". I didnt know there was a connection error by that point.

When I went back to the list of bean types, I found my "Contact block" bean type. But when I went to content > add block, I saw 2 different types with the same name. I changed the name of the bean listed in "Block types", and then the other bean showed up. In that point, I could go on and delete the duplicate.

Minor detail and the scenario is not likely to happen, just though it would be good to add machine name checkup.