Lipsync stuck on last phoneme/blendshape when audio source's audio clip assigned to none

[niiteshk0]

I have added a logic on a button to assign the audio source's audio clip present on the gameobject which has the ulipsync script to none/null, as a way to make the ulipsync 3d avatar stop speaking mid sentence, But there is a bug occuring such that when I execute my logic then the 3d avatar's mouth is left with the last used phoneme/blendshape extended as it was, which gives it a wierd look.

This problem is not occuring in editor but only in webgl builds.

Any help is appreciated.
Thanks!