Whenever I try to mine obsidian, it always reappears when i try to mine it. later in the vid it shows it glitchy
Are you in a protected region that you are not added to? Is it outside the edge of ECC? Was there server lag then (have you tried after a fresh restart)? What tool were you using? There is not enough information in this thread for anyone to help you find an answer... Please provide for information (there is a format in the sticky of this section to help sort out thoughts).
Probably a mixture of lag and server protections for breaking things too fast, etc. You would need to find others with the same pickaxe to really test.