I have a modpack containing Tectonic, Biomes O' Plenty, C2ME (see this modpack), Biome Replacer and Block Swap, and Biome Replacer is only used to remove the Deep Dark, while Block Swap is only for replacing vanilla ores with a denser modded version of them. On one my mod test worlds where I enabled Lost Cities generation (pre-set rarecities), and often around the boundaries of the cities, there would be a large amount of floating blocks creating massive gaps in the ground.

In other test worlds, one under default preset and the other rarecities, chunks would simply not render.

Version?

I have the same problem is there a solution yet?