[Fizzlemizz]

Somewhere, adding the extra lines has created a recursive call that gets back to RepByZone:SwitchedZones()

Simple check, change:

function RepByZone:SwitchedZones()

to:

local count = 0
function RepByZone:SwitchedZones()
count = count + 1
print("count", count)

And see how many times you end up in the same place before it errors.