Since they tested it as compost and not as soil, did they not give you a sheet telling you what to add to improve it like they provide with the standard soil test? If not, that is very frustrating.

Your very high pH probably is behind a lot of your trouble. Over the years we've lowered ours from 8.3 to around 7.0 and the difference in performance is astounding. A high soil pH can interfere in the uptake of nutrients from the growing medium, which might explain the slow growth you were seeing this spring. It doesn't mean the nutrients are not necessarily there, just that the pH is so high that it makes nutrients unavailable to the plant roots.

Most vegetable plants prefer growing in a growing medium with a pH of 6.0-6.5 but they will very readily tolerate a pH of up to 7.5. With a reading of 8.6, it seems you have a lot of amending to do. The best, though slowest, method is to just keeping adding organic matter, year after year, month after month, without fail. Every time I take the time to put another layer of grass clippings or chopped/shredded leaves on top of our garden beds, I know that it will decompose over time and help improve the soil. In our early years I added tons of organic matter, including all the compost I could make, leaf mold, peat moss, chopped/shredded leaves, old rotted/half-decomposed hay, etc. and rototilled it deeply into the ground because I was an impatient gardener and wanted our highly alkaline dense red clay amended yesterday if not sooner. I added other organic amendments that I knew would improve our soil. As time went on, the soil got so much better that now I generally just amend from the top down and let rain, earthworms and other soil-burrowing creatures, and the digging I do while planting simply carry the organic matter from the top down into the lower levels of the soil. I avoid rototilling as much as possible now in order to not harm the earthworms and the microherd of bacteria that inhabit the soil. The microherd of bacteria is what breaks down organic matter into compounds the plant roots can use, and that is one reason why I feel it is important to use Tomato-Tone and Garden-Tone since they contain the bacteria your soil needs.

Remember that amending is non-stop because the limestone in our highly alkaline soil continually, slowly dissolves, raising our soil pH while we are working to lower it. That means that to some extent the amending never ends. If your water is highly alkaline as mine is, that is sort of a double whammy because the water also is countering your efforts to lower your soil pH.

If you have pine needles available to you, that are a great mulch for alkaline soil. They are very slow to decompose, but they will/do eventually decompose, and they help acidify the soil as they break down.

I also don't use much animal manure at all because it tends to be alkaline and my soil needs less alkalinity, not more. I save the animal manure for hugelkultur beds we build in place in eroded gullies and leave there forever to fill in the gullies, heal the land and prevent future erosion. Eventually native wildflowers take root in the healing gullies, largely because I toss handfuls of native wildflower seed in there (sometimes the whole plant tops) after wildflowers in surrounding areas have gone to seed. Of course, the native wildflowers grow here because they tolerate our soil pH so those areas don't need the careful amending of areas where I grow edible crops.

I know you can fix your soil. Remember that sulfur is a great way to lower soil pH too. It takes months to work, so in order to use it to lower your soil pH, add it in late autumn or early winter at the latest so it has time to lower the soil pH before planting time rolls around. Don't get too hung up on the numbers on any soil test. If you were to add nothing but compost, leaf mold and chopped/shredded autumn leaves to your garden soil every year, every nutrient needed by the plants would be available and your soil would become more acidic over time. Just avoid animal manures because they tend to be alkaline, and the one thing your garden doesn't need is more alkalinity.