I have the same problems.
Using Appium 1.7.0/Server v1.9.0 with Robotframework test for Android apps.
I’m using ID locators, ex:
Wait Until Element Is Visible id=${appPackagename}:id/welcome_section_top_empty
When running the test, I get error:
InvalidSelectorException: Message: Locator Strategy 'css selector' is not supported for this session
I tried going back to Appium 1.6.3/Server v1.8.1, but then I have another problem running test for iOS apps. As soon as I start the tests, I get:
WebDriverException: Message: An unknown server-side error occurred while processing the command. Original error: Xcode version '0.0'. Support for Xcode 0.0 is not supported. Please upgrade to version 7.3 or higher
The same iOS test will run fine with Appium 1.7.0/Server v1.9.0