Poisonous concoction visual bug

It doesnt show the red explode animation if i move right after attacking, (life flask charges are being consumed). however if i stand still while attacking it always shows the red animation(if i have flask charges). can someone clarify why this is happening, is it a bug or im missing something?

Adding link to YT which shows the issue :

https://youtu.be/vrqboyJ6eUc?si=cYBv_1Ee5G3Bw4Qi