General DiscussionWhy there was no backdoor??

Backdoor protection has a 15 second delay to put it up again. Did he had creeps in the base before to which he teleported and then were killed?

Backdoor lasts 15-20 seconds after the last creep dies. Maybe that was it. Also base backdoor radius is huge. Covers t2 tower mid completely for radiant.

Gonna add this to luxon's comment above. High ground backdoor falls off NOT when creeps reach hg, but when they reach the flag on the ground in the lane next to hg.

if any creeps reach the big circles in this img backdoor protection of the whole base is removed and it stays like that even after the creeps died for 15 sec

To add to the above, note only ai controlled lane creeps count for BD. If you dominate a enemy lane creep for example he will not count for backdoor removal (he is considered part of the "hero sub faction" instead of the ancient faction). I will suggest to watch the replay and see if it was the case. If you still have doubts you can submit the report to the game support. The new cheat policy is quite harsh if this is the case.