Mixers are a very risky business model and I believe this isn't the first time such thing happens. Back in the time, 6 years ago tho, circa 2017, Bitmixer shut down voluntarily after other services being seized by US government. Bitmixer at that time was extremely popular and their earnings were incredibly high, yet the owners saw that they should stop before being tracked down.
I don't know what's going on right now with Sinbad but I am not very surprised to see that coming. Mixers should take on consideration the risks of running such service and where to operate it.