[2020] Simple Track Editor doesn't let you delete some blocks

Hello, I have the starter edition and was trying to do a map with the simple track editor, I have six block that just can't be deleted anymore. It seems randoms and not releated to a type of block since the stuck block are all different.
I've sent the map to a friend that can access the advanced track editor and he can delete those blocks from there but no way to delete the blocks on simple editor from his account too.

Hope you can fix this asap, even if very limited I would like to create a track with the simple editor, thanks