Error: Unable to find a matching line for sublist locations with key: [locationId]. I am able to upload file without this error, but when another Admin does it, she gets this error, it's odd but was wondering if anyone else experienced that.

Both Administrator Roles? and the exact same CSV? I would start by looking to the Employee records and look for Subsidiary or Locations there. Also Home > Set Preferences > Restrict View would impact a session. Also Subsidiary navigator could be restricting locations.