No MOH from one of two identical inbound routes


I have two inbound routes, configured identically (the target is the same ring group) except for incoming DID number.

On the first one calls come from a sip trunk with a voip provider.
On the second one calls come from a sip trunk with SIPTOSIS software that collect skype calls.

The same ring group is ringing on both trunks incoming calls but only those from the first trunk hear MOH while phones are ringing

Skype callers hear skype progress tone until someone picks a phone.

If I try to set “terminate/place on hold forever” destination on skype inbound route , MOH is heard immediately from skype caller.

It seems like no answer criteria is given back to skype system when MOH starts to play…

Any hint ??

Thank you very much.