I've found the same thing at over 50 batches with the Grainfather, but then why would
Hop experience higher attenuation? But granted, there can be other things that came into play...
I was reading a thread about pH in the science forum. 80% of it was over my head. But there was some discussion about when to measure pH, and relatedly (or not relatedly, depending on who you ask) when conversion occurs. Seems like much of the conversion happens in the first 10 minutes.
That got me thinking about the brulosophy mash temp experiment where nobody could tell the difference between beers mashed at vastly different temps. It made no sense to me because the science must be right. But what if it just took them 5 or 10 minutes to settle at the target mash temp? They may not have really mashed at the temp they thought they did.
Before I had a GF, I did single infusion mash temps in a cooler without recirculating. I frequently over/undershot my mash temp and adjusted. On the other end, I'd typically lose 2 degrees over the course of the mash. But smetimes the temp would then hold for an hour, sometimes I'd lose 6 degrees. If I didn't stir really well, I'd have hot and cold spots, too. Even when I did my best to address these things, there's still so much potential for error. My thermopen is accurate but it only tells me what's happening in the top 4 inches if the mash, and only when I opened my tun to check, which I did as infrequently as possible.
Now with the GF, I mash in at the correct temp, and at worst I see it drop by 1 degree for 2 minutes. And the recirculation should keep it even.
I don't know what the cause is. But my maybe he's just hitting his mash temps for the first time.
It would help to know more about the recipes, yeast, mash temps, fermentation temp/length, OG and FGs.
If he is mashing west coast ipas at 154 and his FGs were around 1.007 and now are 1.012, I'd say he's hitting his mash temps for the first time. But if he's mashing ipas at 148, used to end at 1.012 but is now ending at 1.017, that would suggest a very different problem.