OK, another issue I have seen a lot since I moved to pjsip.
I have found multiple posts about this and think I vaguely understand but I am unsure of exactly how to fix this.
FreePBX 17
Asterisk 20
We do not use Phone Apps or End Point Manager or any commercial modules.
All phones connect via private network through backend VPNs - no general public access to the server.
Grandstream phones configure via tftp from local server. No phonebooks used.
We have Users and Devices as some users have multiple devices.
We have a RingAll group for calls and a BLF-Group group for BLF.
The RingAll group only has actual users, and a destination to the Answerphone on 9999 for no answer.
The BLF has all Extensions including the answerphone.
Very basic - no queues etc.
The desktop Grandstreams - mainly GXP2170s - have their Virtual Multi-Purpose keys set to BLF and the various users eg Key is <user 1001> etc.
The light is BLF and it also acts as a dial key for that user which rings all their devices.
Mobiles use Bria softphone with a very basic SIP setup.
Worked perfectly without errors under SIP.
eg:
Order Mode Account Description Value
2 Busy Lamp Field (BLF) 1 User 1001
6 Busy Lamp Field (BLF) 1 Answerphone *989999
There appears to be no trigger for this. eg here is last night - suddenly every Extension starts trying to subscribe and failis.
[2026-06-15 22:41:30] VERBOSE[5338][C-00000001] pbx.c: Spawn extension (macro-vm, s-CHANUNAVAIL, 2) exited non-zero on ‘PJSIP/8202-00000000’
[2026-06-15 22:41:59] VERBOSE[5097] asterisk.c: Remote UNIX connection disconnected
[2026-06-15 23:22:41] NOTICE[4629] res_pjsip_exten_state.c: Endpoint ‘3010’ state subscription failed: Extension ‘1008’ does not exist in context ‘from-internal’ or has no associated hint
[2026-06-15 23:22:41] NOTICE[4629] res_pjsip_exten_state.c: Endpoint ‘3006’ state subscription failed: Extension ‘1001’ does not exist in context ‘from-internal’ or has no associated hint
[2026-06-15 23:22:41] NOTICE[4629] res_pjsip_exten_state.c: Endpoint ‘1003’ state subscription failed: Extension ‘1003’ does not exist in context ‘from-internal’ or has no associated hint
[2026-06-15 23:22:41] NOTICE[4629] res_pjsip_exten_state.c: Endpoint ‘1003’ state subscription failed: Extension ‘1004’ does not exist in context ‘from-internal’ or has no associated hint
[2026-06-15 23:22:41] NOTICE[4629] res_pjsip_exten_state.c: Endpoint ‘1003’ state subscription failed: Extension ‘1005’ does not exist in context ‘from-internal’ or has no associated hint
I am pretty sure there is something I have missed in the config or something I am doing that I am not meant too.
I don’t understand why it went from working under SIP to not working under PJSIP when nothing changed on the devices. 
Any guidance appreciated.
B. Rgds
John