Doesn’t work between devises – VIZ Manga Review

How come I can’t switch between my phone and Ipad? It says my account is always in the spot I left off on said device. But if I read a ch. at work on my phone my iPad still has me a chapter behind! Fix this! Updated to 2 stars because even though I pay I can only read 100 chapters a day… why?
Review by Kabam ruined it... on VIZ Manga.