Zombie Escape is a very flawed game mode that isn't super fun for a large number of players. To encourage more people to play the game, and not disconnect or go AFK, I suggest that the game mode be changed dramatically.

The common complaints about ZE aren't intrinsic to ZE itself, but rather a result of its mechanical dullness.

Chaining it's maps
The lack of options in ZE's Design

Breaking this down, point by point, the people who play ZS and ZE are looking for fundamentally different experiences, when loading into the server. From my experience, most people, including myself, wouldn't mind playing it every few map rotations. The main issue is when ZE is played, it gathers everyone who enjoys it into one server, and they outvote the people who were already playing, sometimes for hours at a time. Quite frankly, it is really agitating, when the server isn't in the game mode you'd like to be playing, which leads to toxic behaviour on both ends of the spectrum. One solution floating around the community is putting all ZE maps on a cooldown when one is played. While this would solve one issue, it is likely that it would lead to a schism in the community, or an exodus of the ZE fans to another server, neither of which is a favourable outcome.

The second glaring issue with ZE is the lack of agency presented to the players. Zombies have no real options, once they're dead. The only choice for class of zombie is the super zombie, which is not designed for normal play. Super Zombies normally appear at the end of rounds and are suited for this purpose in ZS, to prevent humans from holding out. In ZE, their bulk and lack of other stats are a hindrance. While it is true, that super zombie can both deal and tank a lot of damage, they are leagues behind what humans are capable of. The main issue with the super zombie in ZE is that it lacks any versatility, beyond that. Fast zombies have the ability to jump, and can climb walls to assault skycades, Headcrabs and crawling zombies can get into small gaps the other zombies cannot, super zombies run directly at you, while swinging.

This alone isn't a massive problem, if the maps provide multiple avenues of attack, in lieu of multiple types of zombies to approach in different ways. All of the ZE maps are designed as little more than wide, open hallways, with no other option than to run headfirst into a hail of bullets.

Now, how could it be changed, without removing what people love about it?

Reduce the knockback, and increase the speed of the super zombie
The simplest solution to make playing ZE more interesting. WIth less knockback, and higher speed, the zombies are more credible threats, and the weapons with significant knockback become more valuable to the human's survival. Alone, that would make the gamemode far more tolerable for the people who don't enjoy ZE as is.
Change classes available.
Stepping up in complexity, ZE would be more interesting if There were more types of zombies available to be played if everything else is left as is. Spawning everyone as a boss zombie of their choice would shake up the game mode dramatically, and require a concerted effort from both sides. With some tweaks, allowing a zombie to play a boss of their choice would solve most of the problems presented in ZE, since the bosses are designed to be deadly threats or powerful supports on their own. this would give the zombies a fighting chance when rushing towards an endless hail of bullets coming from the humans, and it would force the fighting between them to be more dynamic, as the zombies and the humans must coordinate amonsgt themselves, or die .
Freshen up the map pool.
The ZE maps in general are all slight variations of long hallways, occasionally with parkour in them. There is little cover, and nothing to think about, when it comes to avenues of attack, jsut a simple push forwards. OBJ maps are a better starting point with this in mind, as they are usually slightly smaller in size, and feature closer-range combat, with varied terrain. Adding maps with more to them than a long series of hallways, would go a long way to making ZE more dynamic, and interesting.

As an aside to that, some of the ZE maps feature sections where the humans fight an NPC boss, while the zombies kick around for 5 minutes, just watching. suffice to say, it is not exactly interesting, when an Anime Swordsman NPC does the killing for the zombies.

Eliminate chaining of ZE
If none of the other options are appealing, then when 2 /3 ZE maps are played consecutively, the rest should be put on a 3-4 round cooldown. This way, people can still play the final fantasy maps consecutively, but ZE will not take over the server for the better part of a day, without removing any of the maps from the pool.