Passive mobs seem to not be spawning at all

currently playing a vanilla plus world with some friends, and recently we noticed at around 5000 block out from spawn there were no passive mobs spawning at all. even when we travelled around 2000m from the point where we initially noticed it, there were still no passive mobs. as far as we can tell, there are no force loaded chunks outside of spawn on the server. my friend stayed at spawn killing animals and I stayed at the area 5000 away flying around to make sure different chunks were simulated, but I was still seeing 0 passive mobs. like none at all. I realize this isn't a lot to go off of, but can anyone help debug? we don't have any mob farms near or at spawn. I don't know too much about debugging minecraft and I am at my wits ends :/