You'll see a lot of that today (as has occurred all winter with the Chicago cluterfudge of weather all year).

What basically happens is the crew's schedule for that day is followed, but bypassing ORD. For example, today there's a Tulsa-Lansing, MI flight that just landed at LAN. The crew was probably supposed to work TUL-ORD-LAN-ORD. Since ORD is 'struggling', United cancels the TUL-ORD, and get the plane to LAN whereas at least one flight can operate.

This probably happens a few times a day in regular operations for one reason or another, but happens several times a day during IRROPS.

While I think of this as "nothing to see here"...I took that TUL-LAN flight and saw it was UA#3201. It's easy to figure out that UA32_ _ is the reserved flight numbers for ExpressJet's positioning flights. You'll see on the app:

Flight #, Routing
3200, Huntsville-Charleston
3201, Aforementioned TUL-LAN
3202, Knoxville-Rochester
3203, Knoxville-Sioux Falls
3204, Allentown-Cedar Rapids

This is just ExpressJet. Skywest uses 13_ _ and some of theirs today are:

1360, Greensboro-Asheville
1361, Flint-Ft Wayne
1362, South Bend-Salina, KS

I see these seemingly unusual flights operating from my home airport, MBS, all the time. Planes coming and going to other Skywest stations, invariably due to ORD issues.

I think mainline uses the low 1300's, but my random checking of the app doesn't show much. I'm sure more 'educated' FTers know how to find everything.