Also running into the problem of two construction ports not docking properly. The very first time they were aligned, the magnets attracted and it stayed that way for a while, until the two ships got further along their orbits. After that one time, they no longer attract. Background: launched a station core around Kerbin with stock docking ports. Launched a second station module with construction ports in a KIS container (after reading the stock port doesn't lock into construction ports.) Used an engineer to replace one of my stock ports with a construction port, and tried to dock the second module (now both ships are using construction ports.) After initial attraction, with no lock, I'm not getting any attraction at all. I've turned snap off on both ports, and slowly increased the force to all the way, trying each increment. I've loaded past saves, even relaunched and attempted to replace again, all with the same result.
The second module's second stage was attached to the payload via construction ports. I undocked the second stage, and sent it back to kerbin to burn up. Does this mean my construction port is now root, and that's why it's not docking to the station core's construction port? How do I tell if this part is root, as opposed to my probe core on the payload being root? Thanks.
edit: Should have said my ksp version is 1.2.2. Also, I'm not getting a "can't merge with root part" error, so I'm not thinking that's the problem. Just want to explore all possibilities. After the initial attraction, when I tried to compress, it told me it can't merge two ports that aren't welded.