Similar issue to this user.

The centre island spawns in perfectly fine, no issues there. However, there's a massive space of void between the center island and the rest of the dimension. I can work around this easily enough with creative mode/Xaero's, but I'd assume that's not an option for those playing on survival.

Past that massive void space, everything generates normally.

Happens with or without any end dimension expansion mods.

Isn't that just.. how the End always works?

From Minecraft's Wiki:

The End consists of one large island surrounded at a distance by many smaller islands, all mainly composed of end stone. There is a gap between the central island and the outer islands of about 1000 blocks with nothing but the void.

The void is expected and this is a non-issue.