I use CCR1036 for NAT functions. The problem is that when you create more than 600,000 of simultaneous connections appear delays, reset the connection. The maximum amount of traffic is 2 gbps. When the load is reduced, conntrack doesn't work in the best way.

Router OS version is 6.7 (There are no information about any changes about tension or performance of this model in change logs.)

Can you fix it ?

You should really move to latest, there is a ton fixed between yours and current latest.