That is because they believed, and then they disbelieved; so their hearts were sealed over, and they do not understand.
The Saheeh International Quran Translation
ذَٰلِكَ بِأَنَّهُمْ ءَامَنُوا۟ ثُمَّ كَفَرُوا۟ فَطُبِعَ عَلَىٰ قُلُوبِهِمْ فَهُمْ لَا يَفْقَهُونَThat is because they believed, and then they disbelieved; so their hearts were sealed over, and they do not understand.