Its like the seismo has to be buffered into the end of the throw animation for it to combo.
Also sometimes after an airthrow I land far away and I won’t get the box dash loop into.
Also online, Viper will literally stand there when I try to seismo L after the throw.
I’ve noticed that I have to begin the “Z” motion once Vip’s feet are on the ground and completing the execution just after she stands up fully erect again. (I said erect, sorry couldn’t help it)
And just as a safety measure I always dash in with Vip prior to seismos off the air throw.
One more thing, you can actually air dash diagonal-down after a air throw higher than normal just height and the seismo will connect to pick it up…(my two cents)
You can buffer it if you can’t get the timing right (it’s a bit different from the air throw), but you can actually do without it if you input it quick enough.
As for the air throw, you will have time to dash forward before doing seismo to box dash. For some reason Viper seems to dash sometimes when I’ve done a ground throw, but it’s still in time for the seismo to connect.
Don’t play Viper online.