Netgear N600 Router After 5 minutes cant hear customer

Hello I’m using Asterisk 1.8 VOIP Sip, I’m having Problems at customers with Router N600 VDSL, that after 4-5 minutes during a call, Customer (that has the router) stops hearing his clients.

I check all over the interent and talked with DSL provider who supply the router (who has no idea was can be problem).
SIP ALG is disabled, And netgear is simple router (not like fortinet) so i dont undestand from where issue can come

Is anynoe experienced it ? Or know about this problem?

Please help


Hello Anyone hear may help please?