I’ve already successfully added interface links via snmp. The problem is when I add an interface link and connect to another router on the map, initially, link Tx and Rx shows the values, then when it refreshes, the values are gone. All become Tx:0 Rx:0… And thats the end of it. It doesn’t refresh. What do I do?
More information required about your configuration. I have few links, which are monitored by SNMP and in 3.5 they works fine.
When I choose an interface and connect a link via snmp v3, initially, values of Tx and Rx shows.

But when it refreshes, from then on it doesn’t retrieve the values already.

Why doesn’t it refresh?
More information is needed about your problem. Maybe step by step instructions.
As I’ve tried SNMPv3 on my Dude and link monitoring is working.