My last few brews have had very low yield to fermenter, primarily due to break and trub left in the kettle--up to 2 gallons' worth!
I'm hitting my target gravities, and getting good yields from my mashes (75%+), with average boil-off and top-up consistent with my pre-brew volume calculations.
I suppose I should be glad that I'm getting really clear beer, but at a 20% loss of product, I'm not very happy about it. I thought perhaps I was using too much rice hull (always keep it below 5%) and perhaps not letting the grain bed settle enough during sparge, so today, I didn't use any. I had a good mash, looked like I got a good clear wort, and I had hopes for a full batch's yield, but no change.
Maybe my crush is too coarse?