Why my messenger suddenly logged out on both devices and can not be re-log in?

My messenger account just suddenly logged out for no reason on both my iphone and ipad. I tried to re-logged in but it wasn't possible, it loaded for a while then back to the sign-in screen. I still can logged in my other account, so I believe it is some sort of account problem rather than the app. My facebook still works normally and I still get messenger notifications quite frequently from my box chat. How can I fix the situation?