1st inconsistent/low efficiency BIAB

Brewed an AIPA this weekend, 5.5gal post boil batch

est OG 1.068, actual OG 1.059

8# 2row
4# vienna
2.5# Rye Malt
12oz Wheat Malt
15.25# total

5g cal chloride + 5.5g gypsum
20qt water; 12qt tap, 8qt RO
30qt aluminum kettle with paint strainer as mash tun

over shot my strike temp a little, doughed in at 167°, temp was 157ish after dough in so i stirred for several minutes until it got down to 153° (stirred this batch more than I ever have before and i normally stir like crazy as it is), put cover on and wrapped in sleeping bag for 60min.

pH was 5.0 = ~5.3 per strip adjustment and was 5.1 = ~ 5.4 after mash

moved from sleeping bag, temp was 149°; put kettle back on the burner for mash out to about 170°

i also had another smaller pot with about 3gal of 170ish water inside to dunk sparge the bag

i normally hit 70% post boil efficiency with the last 5-7 or so AG batches with relatively same method, same grain mill from LHBS, in fact it even seemed like a finer crush this time

i forgot to do a preboil gravity check so I missed the chance to add some DME during the boil but will prob add it to primary today or so

per beersmith my estimated post boil efficient was 60%

any ideas on what could have caused a 10% drop?

i used same grain mill to crush, same equipment, i've done a larger amount of grain before with same system but had slightly lower water ratio to fit it all in

i thought maybe the rye didn't get crushed as well since it's finer but i didn't notice many if any intact rye hulls, also wondering if perhaps rye needs a longer sach. rest and perhaps didn't fully convert?

I've had no problems getting decent efficiency with BIAB. Here are some things I do which may or may not apply...

*I bought a Barley Crusher and set it pretty fine. Finer than you would with a false bottom.
*I check my mash every 15-20 minutes and adjust the temp if I need to. I also stir it up keeping the temperature even throughout.
*I mash out at 168 like you, but hold it for 10 minutes before raising the bag.
*I usually don't sparge.
*If I'm feeling lazy, I'll add an extra pound of base grain and not worry about efficiency.

Where were your volumes compared to Beer Smith? A few quarts off in either direction will screw your efficiency up.

ive done several BIAB mashes with 70% efficiency

recipe and bucket volume were both 5.5 gal give or take

i was talking to the guy at my LHBS at lunch and he mentioned that the drop in temp below 150 may have slowed the conversion and probably would have benefited from a longer sach. rest

i normally do a iodine test but skipped it this time figuring 60min was sufficient