Core show hints issue

Hello to all users!
first of all, i quite new in asterisk / pbx, so please do not shoot me if i ask stupid questions.
Since today i notice that some extensions appear idle, even that they are disconnected. ( i have a php script that use command “core show hints” to display if the extensions are idle. in use, or unavailable.

for example the extension 1201, which is disconnected:
using core show hints

[email protected] : PJSIP/1201&Custom:DN State:Idle Presence:not_set Watchers 0

using pjsip list endpoints

Endpoint: 1201/1201 Unavailable 0 of inf

I use soft-phone (linphone).
I check the extensions, and is configurated exactly like (for example) 1202 which is working ok.

Can you tell me where is the problem?
PS. the system was ok until today. i didn`t change anything . I try tio delete the extension and re-create, restart / reboot. the problem persists…