FeelsBadMan Glad you still ended up winning.
Were you using your Devastating Charge in this clip? It looks like you weren't, but I figured I'd ask because I haven't played Hecarim in awhile. During Devastating Charge, Hecarim becomes ghosted, meaning that he ignores unit collision, which could have expired during or right after Yi's Alpha Strike, causing you to get stuck. While still a bug, it would at least make some sense and you could probably pass that information onto Riot.
Related: I don't have a clip for it, but, playing as Illaoi, if you are positioned a certain way relative to the wall when a tentacle spawns, you will be stuck against the wall and unable to use the back command. You can TP out and you can die, otherwise you are stuck.