I’ve got a few switches daisy chained together with single links and have enabled UplinkFast on them. This switch is not the root bridge; F0/24 is the root port and F0/23 is a blocked alternate port. I’ve got debug spanning-tree uplinkfast on to help out.
SW3#sh span | incl 0/2[34] Fa0/23 Altn BLK 3019 128.23 P2p Fa0/24 Root FWD 3019 128.24 P2p
Now let’s unplug F0/24 and see what happens.