I have this router about 3 months and its was work perfect, connection type is: optic fiber connected to optic transmitter and with RJ-45 CAT6 cable into the roruter VR 600, 

The issue starts about one week ago, every 2-5 min all connection are terminated (cable and wifi) for 1 min or less and then everything continues to work.

The steps i was taken:

Update the router version via admin tool to:  1.6.0 0.9.1 v009e.0 Build 230809 Rel.6944n

its shown that is the last version - same problem

reset the router completely then set configuration again with user name and password (provider) - same problem

reset the router and upload the file backup with all the settings - same problem

configure the optic fiber transmitter with user name and password from provider and connect with cable to PC - works perfect !

so i understand the issue is in my router. what can i do more ?

Thanks

Best Regards Eve.