As seen from the video (sorry for the lag) when start running your cape detaches from the player and magically follows the player
MCPE-221748
Cape detaches from player
Resolved
Duplicate
0
(Unassigned)
Unconfirmed
Multiple
Android 11
1.21.100.20 Preview, 1.21.84 Hotfix, 1.21.82 Hotfix, 1.21.81 Hotfix
Retrieved
This issue will not be fixed, see MCPE-17599.