So recently I've been playing on a 1.16 server and several mobs have been attacking multiple times at once, rather than exhibiting the normal cooldown time after attacks. This has resulted in me dying several times in the server.

For example, I was fighting an Enderman, and his hits were doing damage through my shield, ending with a double-tap that I blocked the first strike of (see video clip). I wasn't able to capture the bleed through damage that occurred, but I did catch the double-tap on the clip. You can hear the shield block sound effect, and then I am killed by a second hit immediately.
https://www.youtube.com/watch?v=Zr9YTEiupH0

Additionally, I have been attacked by a zombie that was moving at normal speed, but hit me six times in a row within a few seconds, killing me (no clip of this one). This one was not lag-induced, however, as when lag happens I always freeze in place before being hit with a flurry of blows.