Thank you for making a bug report!
I have checked the video you have sent and have found the situation that is going on there. In the video you have shown, Overload fusion is fusion summoning the second Chimeratech Overdragon. When the fusion summon is completed, the first thing that happens is Overdragon activates as chain link 1, with the manditory effect to send all other cards you control to the graveyard. Your opponent Chain link 2, to destroy and banish the summoned Overdragon.
This resolves backwards banishing the Overdragon, and sending all the other cards you control, your 2 monsters, to the graveyard.
If you do not believe this is correct or find another scenario where there is a bug, please feel free to let us know and we can investigate the situation. If you believe this to be correct, please mark this as the solution and the topic will automatically close in 24 hours.
In addition, I’d like to recommend you share replay codes in the future as they are helpful by allowing us step to through the gamestate and find out what effects are all in play at any give time.
Thank you for your assistance in helping to check various card effects and making sure everything is working correctly.