Honored Sheikh, May Allah give you Jannatul Firdaus. If someone back then heard a hadith in which a prohibition appeared, and he thought or said, “But why, that doesn’t make sense, that is fair,” and he thought it was kufr, then after a few minutes he changed his opinion — is that kufr?

Ustadh AbdulAziz al-Haqqan

That is waswas and if he suffers from it deeply he should seek out a Muslim trusted doctor.