✖1.Apple Server Issues❌
Apple may temporarily disable the diagnostic function (occurred 2–3 times in the past six months, affecting all users).

✖2.IP Address Restrictions❌
Too many diagnostic attempts from the same IP may block access (solved by switching networks; we maintain multiple dedicated networks for this purpose).

✖3.Weak Network Signal❌
Slow or unstable connections can timeout the diagnosis (fixed by switching to a stronger network).

✖4.Battery Diagnosis Limit❌
Repeated diagnostics (10–15 times) on the same genuine battery may cause it to become undiagnosable.

✖5.Device ID Flagging❌
Frequent diagnostics on the same test phone may get its ID flagged by Apple (we now use multiple test devices to avoid this).

✖6.Locked or Blacklisted Devices❌
iCloud-locked, restricted ID, or blacklisted phones may fail the diagnostic process.

✖7.Modified or Inconsistent Second-Hand Devices❌

✖8.Cheap refurbished phones may fail diagnostics ❌
(1)Serial numbers (three codes) do not match.
(2)Internal components (e.g., logic board) have been replaced.

The above situation is very rare. Usually, if the phone can't run diagnostics, it's a network issue.
Try changing the network or manually enter diagnostic mode. Watch the video below.