You got it on the photos.
As I recall, it was not required to change to non-OPD valves on horizontal tanks because the valve would not work properly. If your tank has been retrofitted with the OPD valve, that could be the issue.
I understand the new Horizontal tanks have the OPD valve, but it is designed differently than the first OPD valves used on vertical tanks.
I have no less than nineteen 5-gallon vertical tanks. Eleven are on equipment and eight are spare tanks. I have been using the OPD tanks since they first came out. None have ever had a sticking valve. I haven't used a horizontal tank since the OPD valves came out.