I have seen this problem before when I was first trying to use the 'nodes' to adjust levels with RB2017 ver7.

I used the Gain Nodes in db as you are doing and had all kinds of trouble with it not saving the set level. I contacted tech support in October of 2017 and they verified the problem. At that time they instructed me to use Volume nodes instead of Gain nodes. And that fixed the problem for me.

I'm now running RB2018 and the Volume nodes work perfect with RB2018 and Windows 7. It may be worth a try to use the Volume Nodes instead of Gain Nodes. The volume node levels range from 0 to 127 max.