I think that was the cause of the problem. Last winter I covered the beds several inches deep with some different composted materials, just to see the effect they'd have. I removed all of that a while back, but there's still a lot of organic material in that top layer.
One bed I covered with well rotted fir tree stump chips and dust that I dug/scraped/broke/shoveled from a rotten stump I found in the woods behind my house.
Another half of a bed I covered with a thick layer of partially composted hardwood leaves, mostly maple leaves. The other half of that bed I covered with well rotted ( 2 years old, the place I bought them from told me) wood compost, pretty much all fine granules.
Plus, there was lots of rain all winter and into the spring, and from what I read that can acidify soils. The Pacific Northwest is an area of the country that typically has acid soil.
So, I think that instead of adding anything, I'll go ahead and remove a couple of inches off the top, down to the good stuff. Then I'll plant some seeds, see how they do, and possibly prove that my theory is correct. The beds will still have plenty of soil. I actually overfilled them when I set them up, leaving no room for yearly topping off with composted material.
I worked too hard mixing compost into the beds so the worms, bacteria and fungus would have a good environment. I'm not going to disturb that by tilling. Maybe that's one reason the deeper soil pH and fertility measured as being good in that area.
Wood chips have a pH level around 4.0. They also rod the immediate soil of nitrogen for the decomposing process. All that would be not good for your plants. Aged, composted, wood chips should be better, but by what you have stated, it seems that the wood chip compost you used has lowered the pH level of your top 2 inches of soil.
My chicken run compost is made up of mostly leaves and grass clippings, with chicken poo as a bonus. I had a base layer of wood chips to begin with, but those have completely vanished over the past 3 years. Anyways, I suspect that the wood chip based compost lowered the pH level of your topsoil.
Although I have tillers, I rarely use them these days. I prefer to garden using the no till method so I don't disturb the soil life. Every once in a while, I take out the battery powered 40v mini tiller to mix up my compost litter really good. It has been a few years since I used my walk behind gas tiller to break new sod for a garden. I think I used it once last year to scratch the topsoil on a larger patch where I had to replant new grass seed.
BTW, I also have a small 18v cultivator, which loosens the soil up nicely in the raised beds without actually tilling the soil. If my garden bed gets too compacted, I'll loosen up the soil with the cultivator. It does a good job for me.