I started playing in 19w08a in this map, mobs spawned sheldom but they did spawn.
When I downloaded the last snapshot no mobs were spawning but the raid mobs with the flag...
I checked the gamerule doMobsSpawn and my difficulty a couplr of times :3
I just wanted to submit this just in case is not a isolated case.
PD: I built a grinder to check if it was a low spawn rate or no spawn rate, no spawnrate is detected