Tower not locking onto me despite clear damage.

I was getting flanked by enemy jungler and planned on executing myself to tower so no one got the gold. I run into t2 tower as jhin, xin zhao is approaching, i throw a W to latch onto tower aggro and die before he can reach me. I hit W, Im well into tower range, yet it keeps attacking minions, ignoring me completely. I tried reaching t3 tower but by then enemy xayah had respawned and got the shutdown on me, luckily we still won cause they had an afk, but this is the type of thing that could make or break a game id say.