Squashed Loaf - Tell me what I'm doing wrong

I've just got in a bunch of new baking equipment and have been trying to adapt an old recipe to work with the new equipment. So far I've had two fails where the loaves have horribly sunken sides. I realize that I could just change one variable at a time until I find the culprit, but I figured that someone more experienced than me might read through this post and see a glaring error in my procedure. If you have a suggestion it could save me multiple misshapen loaves of bread while I grind through all the various permutations.

The old procedure that worked:

The dough was mixed in a Bosch Universal mixer at medium speed for about 8 minutes. Bulk ferment was done in the mixer with the lid on and would typically take about 45-60 minutes. The mixer was then turned on again for 30-60 seconds to knock the dough down. The dough was then formed into two loaves that were about 775 g each. These would be placed into well-oiled 9"x5"x2.75" steel pans with a dark non-stick coating, The dough would then rise for about 45 minutes. After rising, I would score the top of the loaves and bake in a 350-degree F oven for 30-35 minutes and remove when the bread reached an internal temperature of 195-205 degrees F.

The new procedure that results in misshapen loaves:

The dough is mixed in a Sunmix 6 Spiral Mixer. Ingredients are added to the bowl and blended at 70 rpm for 2 minutes. The dough is allowed to hydrate for 10 minutes and is then mixed at 150 rpm for 3 minutes. The dough is allowed to rest for 10 minutes and then mixed for an additional 3 minutes at 150 rpm. The dough is then moved to a 6-quart Cambro box and allowed to bulk ferment until doubled in size. This is taking about an hour, maybe a little more. The dough is then divided into two 900 g loaves. The old bread pans have been replaced by 1/4 size x 4" deep steam table pans made out of 22-gauge stainless steel. Since these aren't non-stick, I've been oiling them and then dusting them with white rice flour before putting the dough in. The dough is then proofed in the loaf pan for about 35 minutes which yields about 70% growth. Once the dough has risen, I score the top of the loaf and then liberally spritz with water. A second steam table pan is placed inverted on top and held in place with binder clips. I’m doing this to promote a high steam environment similar to cooking in a Dutch oven. The covered loaves are placed in a 450-degree oven for 20 minutes at which time the oven temperature is lowered to 350-degrees and the lids are removed. The bread is then baked until an internal temperature of 205-degrees F is reached (25 additional minutes). 

When I remove the bread from the oven it looks beautiful, lots of oven spring and the score mark has opened to the full width of the loaf cap, but the loaf then starts to implode upon itself as it cools. I have cooled it both on a wire rack and in the pan and both methods worked equally poorly. I have also tried poking holes in the crust (6 equally spaced around the perimeter of the loaf cap) using the instant read thermometer thinking that it would allow air to enter the quickly cooling loaf of bread and counteract any vacuum that may be forming within the crust as the bread cools. 

The dough recipe

560 g Water, 105 degrees F

10 g Yeast

45 g Instant Mashed Potato Flakes

60 g 7 Grain Cereal

885 g All Purpose Flour (13.3% protein)

15 g Malt Powder (This is a new addition)

16 g Salt

45 g Powdered Milk

35g Honey

60 g Oil

2 eggs

I look forward to reading your sage advice.