I don't know what the trigger is. I know of 2 people this happened to including me. My CPA mentioned that CA was "very aggressive" & he had dealt with this before. I had already filed in a different state far away from CA for multiple years after moving out. The seizure happened on a Friday late December & my CPA got all of my funds back by the next Tuesday. Did you notify the FTB that you moved out of CA?

Edit

My friend recently had his funds seized from when he moved out for the 2016 year. He got 1/2 back but his paperwork is not in order & got cleaned out. Currently does not have enough to hire a CPA to get the rest.

Btw, I had already done several of the steps listed in https://www.modernfp.com/blog/leaving-ca

I will never move back to CA. Another word of warning from a CHP officer. If you happen to drive in CA as a former resident, make sure you have your out of state license on you. If you forget your wallet, you could be cited for driving with an expired license.