Apex Legends' melee attack mechanics have been controversial for some time now for a number of reasons. The most common of which is that there have been a number of rapid melee glitches that allow players to punch nearly twice as fast as usuals. Most recently Rampart was able to make use of this glitch, but it has been possible on several other legends previously. But recently Reddit user eClics was the unfortunate victim of an entirely new glitch related to melee attacks.
In the clip in question, eClics is running from an enemy and attempts to close a door on his pursuer, blocking her from continuing the chase and giving them time to heal before continuing the fight. But rather than being blocked by the closing door the enemy Loba teleports through the door and punches eClics, ending their run in the game.
The glitch may have been possible due to the lunge mechanic melee attacks have in Apex Legends. This combined with the server issues that players have been having recently would create the perfect storm needed for such a glitch to occur. Respawn has recently pushed out patches intended to fix some of the server issues players have been having.