Unit disappeared after completing an upgrade

Confirmed on gameID=6938841.

My level 1 tactical bomber completed the upgrade to level 3.

I saw the upgrade timer reach 0:00.

The unit was showing a 0:00 timer for a few seconds.

I tapped to select the airplane unit.

This sometimes forces a client/server sync, like when airplanes finish refueling, and stay at 0:00 for a while.

This time, the unit simply disappeared.

I refreshed the Web page.

The unit is still gone.

The unit was far from the battlefield, and there is no record of it in the newspaper.

Note, in case it makes a difference:

Level 3 tactical bomber research completed after I started the level 2 upgrade.