When re-casting Surge on the same target the prurple whirl effects that appear on cast do not appear again. This is because the whirl is basically the "birth animation" of the purple trails following the unit. This means, since recasting only refreshes the buff, they only appear on buff placement.

The purple whirl effect should happen on each cast, and not only on the first cast.

The easiest way to achieve this would be to make Surge remove existing Surge buff on the target(s) first, and the apply a new one. This forces the whirl effect to happen on each cast, since a new buff is placed.

The cleanest way would be to separate the effect into cast and buff, and have the cast particles play on cast and the buff be bound to the buff. This would also fix the cast effect repeating based on vision over the target.