Ring group call pickup issue

Hi, i have a FreePBX with Ring Group 601 for dispatch.

Both exention 2000 and 2001 ring.

2000 dosent have problem.
2001 when it ring, sometime, not always, it does pickup the second line insted of rining line.

both phone are VVX400, same firmware, i changed the phone for a new one, same problem.

any clue? i have been looking for this since a while…