If I was to belt braid with these extra underground pairs, what I was expecting to happen with the generic upgrade planner is underground belt 1 to upgrade to fast underground belt 1, underground belt 2 to upgrade to fast underground belt 2, and underground belt 3 to fast underground belt 3, and so on and so forth.

Instead, the result I got was underground belt 1 to fast underground belt, underground belt 2 to fast underground belt, and underground belt 3 to fast underground belt, when using a generic upgrade planner. As such, factory wide upgrades in this manner breaks this 1-2-3 belt braiding even worse than normal

Also, on a related note, there seems to be an issue with the logistics underground belt names, specificially 'Unknown key: "entity-name.t-underground-belt-#" where # is the number of extra belt.