This is the third knotty issue happened on my Apple devices.
By the end of June this year, my iPhone running iOS11.4 ran nearly 10G of mobile data during a single day. The log of Shadowrocket(An Network Extension app) revealed that my iPhone kept downloading unknown data from gateway.icloud.com at the rate of about 200kb/s. I tried switching the iCloud account, but the problem appeared again after a short period of time. I was busy dealing with the exams at that time, so I simply Rejected gateway.icloud.com in Shadowrocket. No negative influence on daily use.
After some searching, I found some people claimed they have encountered a similar problems (22nd floor): https://www.v2ex.com/t/459452 . However, his solution of logging out of iCloud on macOS devices was not successful for me.
But the trouble didn’t end. Since then, a large number of apps crashes while launching on my iPhone and iPad at a frequency of 2-3 times a week. When the problem occurs, most applications will hang at the Splash Screen and crash after about 10 seconds. Applications that crashed including TIM, Notability and all of the Google apps. WeChat and Apple’s own applications are unaffected. During this time, the phone went hot, and will stuck when entering the iCloud settings. My iPhone runs iOS 11.4 and 12 Public Beta, and iPad running 11.4 and 12 Developer Beta.
I tried rebooting, force rebooting, reinstalling affected apps, upgrading iOS, logging out and logging back in to iCloud, didn’t work. A temporary solution is turning the iCloud Drive switch off and on, which has a chance to temporarily fix the problem. However, entering the iCloud settings at this time has a high probability of being stuck, so you need to try several times. The iPhone will recover from the problem after a while even if not doing anything.