I'm playing on latest update using Android. Hard Tundra with 2 workshops. Notice my chiltin is still 0/16. After this recording, my tank upgrade finished itself under 10s
It was probably caused by me upgrading too fast.
(One ant is busy cooking plate while the current upgrade has already been done => Me accepting another upgrade => Ant bringing that plate to the queen => Stacked upgrade bug
If it's not bug, it's cool having as a feature though, it's cool haha. But yeah