No Guardians in Water Monument

I'm now in the stage of my world where I wanted to build a guardian farm so I set out to find a water monument. Upon arriving I found that the only mobs present were the elder guardians. To find the cause of this issue, I loaded the world in 1.15.2, and there plenty of guardians. I began to search online for helpful instructions such as set "doMobSpawning" to true, lighting up caves in spectator, but nothing seemed to works. I checked three other monuments in the world and they all had the same issue of no guardian spawns.