Log-File Presence Warnings

Hi there.

i have a lot of Sangoma S500 phones, and my logs are getting flooded with the following messages for every extension:

NOTICE[29794]: res_pjsip_exten_state.c:358 new_subscribe: Extension state subscription failed: Extension 9924*1000716 does not exist in context ‘from-internal’ or has no associated hint

unfortunately i cant spot any misconfiguration.
all relevant asterisk modules should be loaded, the extensions are in the right context.
does somebody have a clue from where this could come?