I have 3 very large vertex frontiers setup but they only render when standing in certain parts of the world.

here is the red one unrendering on the minimap once i get far enough north

it still properly shows the title when walking through the border, its just a rendering issue,

Minecraft 1.21.1
Neoforge 21.1.73
MapFrontiers-1.21-2.6.0p2-neoforge

if there is any more info i can get you please let me know :)