Troubles with Priority Group activations after upgrading from 11.4.1HF4 to 11.4.1HF6

I think your load balancing method might be an issue. You need to be using a Ratio LB method for the value to be significant. Try it like this:

ltm pool lbtest_3306 {
    load-balancing-mode dynamic-ratio-member
    members {
        server1:mysql {
            address 10.19.1.41
            priority-group 100
            session monitor-enabled
            state up
        }
        server2:mysql {
            address 10.19.1.42
            priority-group 1
            session monitor-enabled
            state up
        }
    }
    min-active-members 1
    monitor tcp
}

Cheers, Mike