How to fix difficulty glitch in the nether?

I opened a server to test out a plugin that I coded and some friends happened to join because the whitelist was off. They insisted we play normal survival, so I listened, because my plugin was more for convenience than for fun.

When we entered the nether, we noticed there was an inherent lack of mobs and we just kept roaming around in search of a nether foretress. We noticed the piglins weren’t aggroing, despite our lack of gold armor or distracting gold ingots, so I went into creative mode and attempted to spawn mobs in the nether, which failed as they all vanished. I went to check the difficulty and it said it was in Normal (and I made sure of it by doing /difficulty normal). Despite this, the mobs weren’t spawning, and eventually the difficulty swapped back to peaceful.

Then, I went to the overworld and proceeded to spawn zoglins, which succeeded, so I checked the difficulty and it was in normal. I know this glitch wasn’t caused by the nether portal being formed because I remember clearly my friends dying numerous times to creepers in the overworld, so I have no clue why this is happening. I do remember creating the world in peaceful by mistake though so that could be a factor. The gamerule mobSpawning is on.