This happens when they exit cm/mz, someone else deletes the member they were last on
Simple fix for customer or support:
1: Click on any non-member module
2: Click the find > members button
3: Select any member on the list
Members module should load with an existing member and work correctly
OR (This is just for CS Reps)
Go to setup on left hand menu > under Association Options > Support staff only: Admin Consolel > Find MEMBERS: Fix null company name; run the backup and execute the primary query button.