If the alignment keeps changing, you have worn part(s) or something is loose. Toe-in normally changes as the front end ride height changes, caused usually by springs sagging or when a new lift installed.
Once set, the alignment should hold for a long time, as long as the front end isn't seriously abused. If it keeps changing, you need to find out what is loose or worn.
Assuming it the alignment was done in a shop, the tech should have inspected everything in the front end to find worn parts that would prevent the alignment from holding.