A user cannot upload files to corporate servers from their mobile device when outside the...

Comprehensive and Detailed Explanation From Exact Extract:

If uploading fails only offsite,mobile data limits or restrictionsare the likely cause. Data caps or network management can interfere with uploads.

FromTravis Everett – All-in-One Exam Guide:

“When mobile users experience network issues, always check if the device has reached a data cap or roaming restriction.”