While reading Important Upgrade Notes:
I found this :
USB devices (Wi-Fi dongle, Bluetooth dongle, 3G/4G dongle, USB DAC/speaker, and DTV dongle) are no longer supported.
If your Synology NAS is currently connected via a wireless dongle, it will be disconnected after the update.
Could this be the cause that we can't update from DSM 6.2.3-25426 and above due to the update breaking all USB devices, so that means the Loader will not load !
Hmmmm
What do you think ?