Bill,
If you had the ST4000, I would tell you that the very very small roll pin (about the diameter of a pencil lead) that holds the tension lever on its shaft had sheared, and the shaft has oversized the hole in the tension lever, and therefore the tension lever is not engaging the inside cam.  But......you don't have the ST4000.  Perhaps the SPX-5 is constructed in a similar manner?  I'm just guessing, because I've never seen one up close, but at least this gives you something to look for.  I'd suggest taking the AP off the wheel, splitting it in two to look at the insides, and operate the tension lever while watching the inside cam.  Hope it helps.

Hello Bill,

I had a similar problem with my ST 6000 wheel pilot (I believe the HW is identical). After a fairly short period of time, the tension arm would disengage. I removed the unit and tried tightening the cam mechanism plus anything else that would help keep tension on the belt without much success. The problem persisted so I ended up using shock cord to keep the arm engaged. My unit is older and over time I think the plastic parts wear and lose their tolerance. Replacement of the cam and belt may be the only fix. I plan to send mine to Raymarine Service then keep it as a backup.  The wheel pilot is marginal for the 36 so I upgraded to the below deck linear drive which works much better. Because your unit is new, chances are that all it needs is adjustment. Eventually, however, it will probably slip again. I suggest the Raymarine knowledge base (there is a lot of good information there) or emailing their tech support. I wager this is a common problem.

Regards,
John