Hostile Mobs Not Spawning

After a few hours of playing on my friend's server, I noticed that I had seen very little hostile mobs around. I asked my friend if he had changed the settings and he said no. We waited till night time and saw nothing but a few pillagers. When I had searched for a solution or explanation for it, I saw that it was possibly caused by traveling distanced by different nether portals. I have seen no hostile mobs still and thought it may be a bug.