Not from my experience! I've used 5x multiplier on 3+ accounts so far and have only received ONE instant ban - from using the multiplier during Journey. Maybe you did something else that triggered the instant ban? Or perhaps you used too many Sparks in a row that you triggered a check on your account. I don't know for certain, but I've mostly been using enough sparks to open 2-3 times, then doing pvp for a while, or summoning, and then going back to spend more sparks after a small amount of time has passed.
I have, however, NEVER opened more than 2-3 of the "bonus" chests from the events on the same day (The ones that have the greatest chances of Legendaries).