When I cloned ODK-X Services this happened, though I didn't change anything

D:\ODK-X Services\services\services_app\src\main\java\org\opendatakit\services\MainActivity.java:326: error: cannot find symbol
symbol: variable KEY_CURRENT_USER_STATE
location: class CommonToolProperties

This is currently an issue because the remote repository and build system are undergoing a major overall. This means that for the next month or so you have to check out any ODK-X dependency locally because the remote library is not available. NOTE: dependencies that are NOT part of the ODK-X project are likely not effected because they have their own artifact hosting system.

In the case of Services, the README discusses the dependency on ODK-X androidlibrary.

The error you are seeing is the compiler is looking for state variables defined in ODK-X androidlibrary. Until the libraries are available in a remote repository again, you need to checkout ODK-X depdendencies into the same folder and the build scripts will import the code and compile it.