I've got a problem on a QuadroM8L with Aastra 6757i :
inbound calls dropped after 50s when put on hold
while intern calls or outbound calls can last much more on hold…

Is there something I'm missing ?

Hold is done by picking another line on the phone (4 IP lines are available on each phone),
extensions are local and there isn't any problem to transfer the caller to any extension.

Thanks in advance.