My phone was also a XT1600, but I had a TIM chip. Since this phone is now a backup phone (I have a Poco X3 Pro now), I haven't had the chance to test eventual modem failures.@jeferson1979 , no luck for him. His phone is an XT1600, which is one of the dual SIM models. He tried a dirty flash, but it made no difference.
What APN settings work for you with Vivo?