I have narrowed down the circumstances where this happens. But I can't get it to reproduce the error consistently. Here's what I can say:
1. It has something to do with running a feature that uses the same pump as the "Pool" but the feature itself does not actually turn on the "Pool body" or requires the pool body to be on.
2. I can get the error when the Pool is on, and the feature is on.... then, the Pool is either turned off manually, per schedule, or by switching to Spa. However, the same Pump remains on as it is necessary for the Spa and/or the feature.
3. Then, the Pool gets turned on again... either manually or by schedule... It could be the Pool body itself that gets turned on, or a feature that uses the pool body. In such cases, the Pool body get's turned on, but the pool pump relay (that in my system, only powers the SWG) does NOT always get turned on with the pool. The end result is the Pool Body is shown as on, the Pool Pump relay is off, and thus my SWG is off during that time.
4. I'll also add that during Spa operation, the relay is on as SWG feeds the spa. So another way to look at this is when the SPA get's turned off, the relay get's turned off with it, but subsequently turning on the Pool body (under certain criteria) doesn't always turn that relay back on. I say this because my heater does this unpredictably too. In that the Intellicenter (NOT the heater's flow switch) will turn off the heater when switching between pool and spa (but not always). It does however turn itself on again after the set delay very reliably (if it happened to turn it off in between switching). But there seems to be logic in the INtellicenter that says, Spa Mode off thus Heater Mode Off... without thinking that the mode it's switching to (the Pool) will also need the Heater, and there isn't a need to turn it off.
I know this sounds like a lot of back and forth, but in my pool, it is all necessary to circulate water through all the pipes, returns and main drains.