Removing the FTB Chunks mod resolved the issue but I wished to keep the chunk claiming feature so this was undesirable. I was able to work around the issue by removing the chunks.dat file located in minecraft/world/data/. That file appears to store the data for which chunks should be ...
There are manual fixes to this, rolling back the ./server/world/FTBTeams/ folder and deleting the ./server/world/data/chunks.dat file (alongside unclaiming every ftb chunks claim), however these are completely manual which requires server administration to manually perform these actions each time...