There are loads of posts just below yours asking the same question to the same problem. Have you opened any to see if the helpful answers may apply to your problem ?
If you just scroll deown below "post an answer "you will see the first post from Caran. There are another 5 ending with Daij All ask the same question as yours.
Next time you sign in check below your password ro see whether the 'Remember me on this computer' box is ticked. If not, then tick it. If it is ticked then you need to check your browser settings (there is usually an option to remember passwords). It could also be that you are clearing your cache/browser history when you log off. Or if someone else uses your computer they may be deleting the history each time they log out.
Fiction, only me using this iPad or anything else here.
But you are all correct that I should have checked previous answers first.
Tend to just leap in.