He's been there what, 5 days? Things were blissful for Tuchel at Chelsea the first 12 months. But soon after that articles kept coming out about how players felt drained by approach and once the ownership change happened, he struggled to get along with the new owners too. It wouldn't surprise me at all if there was friction between him and the Bayern board/players in about 18 months.
I personally wouldn't have sacked him. He's a great coach but him being difficult to work with has been well documented since his Dortmund days.