What is the reason?

[~rp]

one of the available options at User CP is :

Automatically accept buddy requests

if that is selected (even by mistake) then Buddy
requests are accepted without user's consent.

any user can disable receiving PMs at any time.
we do not know the reason unless user informs.

Let us hope that concerned member sees this topic
& enlightens us with the reason for disabling PMs

Let us wait with patience.