Here's a new "well, that's broken"... anyone care to posit what the trigger was?

Have a very simple 2-segment PNR, both on Mesa and the first half of which was flown today, landing 20+ minutes early. The return will be flown Wednesday and is showing on time. No changes have been made to this one since booking (a minor miracle in and of itself)

I just got both a text ("We're sorry about the changes to your travel plans. We'd like to help by providing a meal voucher for everyone on your trip. See your meal vouchers here: (URL) Confirmation Number: (The PNR for today's trip)") and an email with the actual voucher in it-- I've gotten the texts before but this is the first time (IIRC) that an email has accompanied.

This, of course, alarmed me that there was something wrong with either my reservation or the return had been pre-canceled or something... But...as far as I can tell not only is absolutely nothing wrong with my specific reservation, nothing is wrong with any of the flights between my city pairs today (in either direction)

Any idea what triggered this (and if there's anything else I need to check)?

Of course since it seems UA has nothing to apologize for I have no intention of actually redeeming but am curious...