???Really? IME it is not at all common for UA to operate two versions of the exact same flight, same city pairs, with same flight number on the same day. Ordinarily, UA would operate the make-up flight with a 2000 flight number to avoid confusing its systems.

This has completely confused UA's systems. For example, the App thinks the aircraft which will operate UA837 SFO-NRT this morning is still at ORD.

Further, there appears to have been a diversion on one of these flights to ORD, which is apparently why Flightaware shows the first departing from Fond du Lac rather than FRA.