Consider adding -debug to the end of the command line that you use to open PowerCivil. This will create a file, the path to which is provided in the last line after loading everything. Open that file. Look for all instances of CIVIL_XIN_FILE to see how it is specified.
That should reveal to you how that variable is set, and should get you closer to finding out why it might be reset.
That should reveal to you how that variable is set, and should get you closer to finding out why it might be reset.