I had this problem as soon as I upgraded to 2.1.6 some time ago (I have OS hardware 2.0, AC and one expansion board). I just upgraded to firmware 2.1.7 and the problem persists.
On the expansion board, stations 1, 4, 6 and 7 are permanently off. Valves will never open.
Expansion board stations 2, 3, 5 and 8 are permanently on. As soon as a valve is hooked up, it opens.
Stations 1 thru 8 on the OS module work fine.
I don’t know if my expansion board has failed or if there is some incompatibility with firmware 2.1.6 and 2.1.7. I didn’t report this until now because I only used one station on the expansion board and that zone was not used very much. But now I need it and more.