The only time I have seen this happen is if one has changed one's store password does not match what the e-mail server knows about, which will trigger the dialog for password entry. Generally there is a checkbox in that dialog that says, "Remember password," or something very similar after the text box in which the password is entered.
If you type in your current password, and it's been being accepted, then make sure the next time the dialog presents itself you hunt for that checkbox and make sure it's checked.
Brian - Windows 10 Pro, 64-Bit, Version 1909, Build 18363
Tolerance is the positive and cordial effort to understand another's beliefs, practices, and habits without necessarily sharing or accepting them.
~ Joshua Liebman