and 40km working distance is normal.
I'm surprised that is the standard. With the placement of most cabinets, I'd have thought the 10km standard would work just fine, with only a few cabinets needing 40km.
For the original poster, there are multiple standards for carrying the signal over fibre - and the one used to communicate with cabinets uses a variant known as 1000base-BX. Most hardware uses pluggable interfaces to determine which variant - which is where the SFP modules come in.
1000base-BX itself can handle different distances, of 10km, 40km and 80km, but requires SFPs with different capabilities.
I guess the delay is because the cabinet came installed with an SFP only capable of 10km, and communication is proving unreliable, so 40km hardware needs to be put in place. I guess it comes down to the cost.