custom-command-issue.js

// wdio.conf.js
{
	...
	before() {
		browser.addCommand('foo', function (callback) {
			callback.apply(this, [])
		})
	}
	...
}

// test.js
it('should succeed in selecting the body after being selected in a built-in command', function () {
	browser.waitUntil(() => {
		expect($('body').state).to.equal('success')
		return true
	})
	expect($('body').state).to.equal('success')
})
	
it('should fail to select the body after being selected in a custom command', function () {
	browser.foo(() => expect($('body').state).to.equal('success'))
	expect($('body').state).to.equal('failure')
})

I don't think this would work cause the expect assertion would throw exception itself. You can do something similar like this:
browser.waitUntil(() => {
return $('body').state === 'success';
});