When you say extension tree expert I wonder if this was the Cooperative extension service? I am surprised that they gave you so much information from these pictures, and did not ask for samples to be cultured. Though some of the damage in the pictures looks mechanical and no problem, some resemble cankers. I can't tell by these pictures. Also how are they planted? Are the root collars visible or are they buried too deep as are 90% or better of trees on landscapes? Anyway these do look like poor trees and you might be looking at getting that warranty from Lowes. And never ever fertilize a sick tree before you know the problem. Some diseases like a good fertilizing. Also never fertilize a newly planted tree for at least one full growing season, two is better. Here is a link that might be useful: Some cankers of Maples

I've never heard of Southwestern disease so can't help you there. It's normal for bark to crack and come loose as the tree grows. That's how the trunk expands. On mammals the skin stretches. Insects and other arthropods shed their skins to make room to grow. Trees pop their bark loose. Earwigs are not going to invade your tree. They're just sheltering under there. Tree boring insects don't need the bark to crack to get in, the females have drills for ovipositors and they drill holes through the bark and into the wood to lay the eggs that will hatch into wood boring larvae. If you're seeing the new cracks in spring then it's not the hot summer sun, it's winter cold. Whitewash won't help that, but you can get tree wrapping tape for protecting from winter cold. Earwigs will still get under it though. And you have to make sure to take it off in spring so you don't strangle the tree when it tries to grow. Dont' peel off cracked bark. It's still serving a purpose so long as it stays on by itself. Leave the tree alone, that's my recommendation.

Sun burn could cause this as well. Given the canopy cut, that is definitely a possibility. If that is the primary cause, paint with a diluted latex paint. When did the bark damage show up? The upper picture is more recent as the trunk picture had calloused over along the at least part of the damage. Since it is at ground level, one of the problems is that the core wood will attract pests - that eat the wood, or eat the rotting wood. If the base trunk has been that way for quite some time, you may have some pests within the wood, contributing to issues.

Thank you so much for all the helpful information. I really appreciate it. I'm definitely going to check on the roots later this week when I get the new soil. Until then I won't disturb them. So true about not really knowing what conditions these plants were grown in. I got all but one(potted) from a nursery on Etsy in Southern California. The smallest one came (unpotted) was a gift with seeds from another Etsy seller, and is approximately 5-7months old so I don't think it would have split yet. All the roots seemed relatively healthy when unpotting them, and they had already split because the old leaves flaked right off. However, I'm pretty sure the one that looks like it is having a rot problem came with significantly shorter roots than all others. Unfortunately, I already ordered more in the mail from the same seller because I'm impulsive. Maybe I won't unpot them for awhile and see how they do.