Using PHD2 tonight went very well with Ekos while imaging, so I experimented more thinking the subframe setting within PHD2 may allow for less processing on the RPI3.

I checked the Use Subframe checkbox on Camera tab in PHD2 while guiding with an ASI224MM-c.

It immediately crashed Kstars/Ekos without log entry. PHD2 and indiserver remained running. Restarting KStars and reconnecting worked fine as if there was never a beat missed. To reconnect though, PHD2 had to complete stop guiding before restarting KStars. Once restarted, all worked again.

Any idea? Is it worth getting this to work, or would there be no benefit?

It is reproducible with just looping. I can try to see if I can catch a log if needed.