The iPhone X’s early teething troubles have largely gone away, but there’s a lingering problem for some owners… and it’s a fairly serious one. Users have reported that the iPhone X’s touchscreen won’t turn on for several seconds when there’s an incoming call, preventing them from answering or seeing who’s on the other line. Complaints started surfacing in December, but the issue has persisted until now.
Source: iPhone X owners report trouble answering phone calls