Low Pre-boil Gravity (pH issue?)

Hi all, I've made a few all-grain batches and I've never had any real issues hitting my numbers (I use BeerSmith). I'm very familiar with the software and hit all my normal variables that usually affect preboil gravity (temp, vol, crush, time, etc.). Thus I was shocked this weekend when I was shooting for 1.065 and got 1.038....here is my grain bill:

12# Pale 2-Row (@ mash)
3# rolled oats (@ mash)
1# victory (@ mash)
2# roasted barley (@ vorlauf - fly sparge)
1# chocolate (@ vorlauf - fly sparge)

The rolled oats are at about 15% of my grain bill, so I mashed for almost 2 hours to ensure conversion (they have 0 DP, so they utilized the 2-row for conversion). I mashed at 153 F. There are only a couple reasons I came up with:

1. Mash pH too high: I've never done any water calcs/additions since I've never had a problem with water before (though I've never brewed at this location, so that changes things). The water I used has a pH of 7.5 per water report (city water, not well water, so report should be accurate). I know ideally mash pH should be 5.1 - 5.6, so I'm worried that the pale grains I mashed with might not be enough to bring it down this low (does anyone know for sure based on the grain bill above?). I know the dark grains may have helped me if this is the issue because they're more acidic, but I was following Gordon Strong's advice of adding at vorlauf (never had issues with this before).

2. I added the oats to the top of the mash (after the pale and victory), but stirred well I believe- perhaps I didn't stir enough ensuring that they're in contact with the 2-row for good conversion?

Anyhow, I was wayyyyy off my target. Based on the above information (tried to get it all here since I know most answers are just more questions usually haha), does anyone have any ideas that I don't or should I start thinking about water adjustments....would a slightly high pH really throw it off that much? Thank you.

 

Thank you all for your input. @DunkelFester I don't believe any of those are an issue for me. I adjusted the temps for my ATC refractometer into its range (I also checked a few readings with my hydrometer side-by-side to make sure it didn't need calibrating). Both the grain mill and scale I used were those of my local homebrew shop and they're very good, so I doubt those pieces of equipment were off (though it's possible). I've used them plenty of times before though and never had a problem. Regarding over-sparging - I used the water volumes in beersmith for the grain bill I had (7 gallons in mash tun and sparging with 4.5 gallons in HLT for a pre-boil volume of 8.25 gallons). In terms of the water I used, as I mentioned a pH of 7.5 and I know it's very soft water 14 mg/L (where I've seen that 0-60 mg/L is very soft). The only thing any of you mentioned that I'm not sure about is the thermometer - I'll check it to see if it needs calibrating (I doubt its very far off though).