I'm hosting the server myself, but this same issue also occurs on, say, aternos.
The server has 8gb alloc. ram, 6gbminimum, (pc has 16gb total), intel i5 12th gen, rtx 2050, the 2nd pc im joining the server with is even better.
A modpack with just Biomes 'o Plenty (and terrablender) and the Changed Mod 0.13 will sometimes fail to load newly-generated chunks. Reloading the chunk by rejoining or by moving away and then coming back (i do this by tping) fixes it. reloading chunks with f3+a does not fix it. This never occurs in singleplayer, only on servers. I can provide the server's log and other files upon request. See https://youtu.be/ZE2NwA0w3Pw for demonstration of the bug.
Apparently this only occurs with 0.13, earlier versions are fine.
Changed mod's config file's bottom three settings, fastandcheap as well as two other cache related configs, do not fix this when toggled.

Those configs only affect resource loading speed, when the game launches.

After looking into this issue, I've determined the actual incompatibility is TerraBlender. I've had reports before about how TerraBlender was eating up all of a servers RAM.

I take it back. After testing, this issue does not happen with only TerraBlender

I think you were actually right the whole time with the issue being terrablender. Although a modpack with just terrablender and other, non-biome mods in it wont have any problems, terrablender + any biome adding mod (i used terralith, which doesnt use terrablender) + changed produces this issue.
Strangely, removing changed resolves the terrablender issue, so I dont know what's up with that. It seems like something about terrablender + a biome adding mod + changed makes the server have a heart attack. I hope that this helps you narrow down the issue.

Also, I deleted some old, unused configs the server had, and the issue with biomes 'o plenty has changed a bit... Still is a problem though. Explained in the video. I get confused by my own minimap and lie at 2:03. More terrain DOES generate than before but its not that ocean. https://youtu.be/ZCQqRvudtm8?si=C3I0I_r5FqURdCVD

Perhaps the workaround/fix for this would be to scrap Changed's compatibility with Terrablender,as relatively no one utilizes purely the two together but rather some other,larger biome mods like BYG or BoP in the mix.Though it's also to note that this issue came around 0.13 instead,whereas in 0.12 and earlier it wouldn't have taken place at all.

I went to the mcmod site and found that people weren't that impressed with the mod （Terrablender）.

I quote this comment, "Folks, be aware that in version 1.18.2 if you're using a server that is cat or a-side using the MV Multi-Worlds plugin to generate worlds will result in a generated world that has no trees, no grass, no anything but squares (seems to be the case with all plugin+mod hybrids)."

Maybe the mechanics of the module should be looked into...