You could try the (app's) settings
> Settings > Message notifications >...
as shown in my first screenshot.
In addition to that please check if there are
no 'account-specific' settings (unintentionally)
> Long-press on account name > Special settings > Message notifications >
Disable 'Special settings': togle the button to the left
[
Repeat this for each account]
as shown in my second screenshot.
The result should be the same behavior "as any other app does"