I am using a Belkin F8M747bt Qi charger (not the expensive one from the Apple store) in combination with an iPhone X (iOS 11.2.1). I have also the issue that when the iPhone is fully charged, the Belkin keeps indicating that it is charging (flashing green led), while it should go to steady green. Also the battery indicator on the Phone is still containing the flash symbol at 100%.
The Belkin manual states:
Qi device is detected.
Solid – fully charged.
NOTE: Your device must support a full battery communication to the base station for the LED to turn solid. Otherwise, check the Full battery indicator on your smartphone.
Blinking – charging in progress.
My conclusion is that the current iOS versions are not supporting this communication (yet) or the phone is failing to detect the correct level to send this command to the basestation. Other Phones are probably doing this right already.
I hope it will be solved by an iOS update. Even it is just a little bit annoying.