Is a son considered disobedient to his mother if he is compelled to work in another country to secure their expenses, and he visits her annually and hosts her, while his mother is alone and affected by his absence?

As long as you need to work in another country due to the unavailability of suitable work in your own country, you are excused, and this does not constitute disobedience to your mother. Strive to be dutiful to your mother and treat her kindly, with sincere intention for the sake of Allah. For being dutiful to one's mother is among the best acts of drawing closer to Allah and among the deeds most beloved to Him.