Major system errors usually cause apps or iOS to suddenly act up and stop working. Among the common symptoms to occur would include but not limited to constant lags, random restarts, and unresponsive or stuck displays. Aside from system errors, memory-related issues including insufficient or low internal memory can also trigger occurrence of similar symptoms.
boot up issue
When an iPhone suddenly gets stuck during start-up, it means that something is ruining its boot-up sequence and unable to go through. Oftentimes, such problem is attributed to major system errors from bad apps, malwares, and data corruption. In other cases, stuck issues are tied to memory problems like insufficient storage and other memory-related errors.