bread collapses in the oven

After nearly ten years of baking bread I ran into a problem with rising.  My method has not changed but my brand of flour has.  I think I'm using a good quality flour but, due to covid19 and the store shelves, I'm locked into using a different brand and sometimes type of flour.
I have used, exclusively, King Arthur Bread Flour in combination with either King Arthur Whole Wheat or Bob's Red Mill Whole Wheat.  My yeast is an instant yeast I buy by the pound from Gordon's Food Services and is apparently the same as sold in King Arthur's catalog.  All other ingredients remain the same brands I buy off the shelf at the local grocers.
My process is to mix sugar, brown sugar, molasses, butter, a cup and a half of oatmeal with a cup of near boiling water (to partially cook the oatmeal) in a stand mixer for five minutes, cooling the mix with two more cups of room temperature water, bringing the mix down to my skin temperature.  At this point I add the whole wheat, a cup and a half, and then about four packets of yeast.  All of these ingredients are measured by scale in metric.  I begin incorporating the bread flour and some wheat germ and another cup of room temperature water and salt, mixing until the dough begins to pull away and form a ball.
I remove the dough and let it rest about twenty minutes under cover.  I hand knead the dough for about another five minutes, cloak it, and let it rest about 45 minutes in a protected spot, usually the oven, warmed depending upon the season and kitchen conditions.  (I pre-warm the oven by setting the temperature at 190F and turning it on for one minute.  I use four pottery loaf pans, and these are kept in the oven along with the rising dough.  I have done it this way for ten years and achieve a good rise and flavor.  I use the wheat germ for a higher gluten, believing that this reduces the crumbling of the finished bread.
If the resting dough has doubled or more in 45 minutes, I remove it and knead it a short time, usually not more than three minutes, and return it to the oven for another 45 minute rest.
After doubling, I remove the dough and portion it into four equally sized loaves and place them in the pans and return them to the oven for another rest until they double, about 30-4o minutes, covered with a towel.  If I'm satisfied with the rise, I'll remove the towel and set the oven for 365F or 375F and let the oven achieve temperature, the whole baking process from cold to completion is usually 33 - 37 minutes.  I experience a further rise at this point until the loaves are three times the size from when I first introduced them into the pans.
I remove them from the oven when I'm satisfied they're done and have achieved an internal temperature of 195F.  I remove them from the pans unto a cooling rack, usually on their sides, and cover them snugly for cooling. 
For ten years I've done this with good results and nice 1-1/2 lb loaves with good flavor and texture.  I've varied little from this process, but my last two bakings have left me puzzled.
My first and second fermentations have met expectations -- a good rise and development of yeast smell.  My loaf fermentations, however, have not quite met expectations but have at least risen to nearly twice.  After baking, however, the loaves shrank somewhat and came out barely bigger than what I placed in the pans.  I had thought that the yeast had gotten old or had been older when I bought it, so I replaced  the yeast with ordinary packets of instant rise yeast  (4) this last time.  The same thing happened -- all appeared well, smelled well, felt well during kneading, but the loaves failed to rise and even shrank somewhat in the baking.
I tested the oven and found nothing wrong or out of order.  The only major change was going from King Arthur Bread Flour to Ceresota unbleached all-purpose (the only available flour) in these last two bakings. 
I find it difficult to accept that minor difference in the flours would produce such a change.  I can produce the recipe; all ingredients are weighed.
I could really use some help here; my family loves my bread, and I do, too -- until now.