This is the 3282nd most frequent Russian word.
остался
"Остался" - "remained" or "stayed."
Here 'остались' refers to something remaining or being left behind.
Остались только несколько яблок на столе.
Only a few apples were left on the table.
Here 'остался' means 'stayed' and it is used to describe the action of remaining in place.
Я остался дома, потому что шел дождь.
I stayed home because it was raining.
In this context, 'осталась' is used in a metaphorical sense to indicate that an issue persisted.