babel/packages/babel-preset-env/test/fixtures/loose-class-features-precedence/properties-and-methods-not-loose-preset-loose/stderr.txt

Though the "loose" option was set to "true" in your @babel/preset-env config, it will not be used for @babel/plugin-transform-private-property-in-object since the "loose" mode option was set to "false" for @babel/plugin-transform-private-methods.
The "loose" option must be the same for @babel/plugin-transform-class-properties, @babel/plugin-transform-private-methods and @babel/plugin-transform-private-property-in-object (when they are enabled): you can silence this warning by explicitly adding
	["@babel/plugin-transform-private-property-in-object", { "loose": false }]
to the "plugins" section of your Babel config.