Some iPhone X users are unable to answer calls because their phone displays aren’t waking up when a call comes in, The Financial Times reports. Users report that the ringtone will play for an incoming call, but the screen won’t wake up for several seconds, sometimes resulting in a missed call. A restart seems to resolve the problem temporarily, but after 15 to 20 calls the problem reappears. Users who have had their iPhone X replaced by Apple are reporting the same issues with the replacement units, but it’s still unclear whether a hardware or software problem is to blame. Apple is “looking into these reports,” but hasn’t provided any further information on a fix.