After Thaviks disappear and goes invisible after taking damage, it is possible to see him climbing the walls on the arena. If you shoot him, he will fall off and instantly die, ending the strike
Video proof: https://youtu.be/eCRjzlDBuCY
I assume this is a cheese.
[spoiler]Video not mine[/spoiler]
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That's because you were fighting French Thaviks. American Thaviks is harder to kill.