My 51822 device can be discovered but can't be connected

[Hamber]

dear all I have two same 51 822 device with same program, one is normal, the other can't be connected even re-power manually .The two all can be found by nrf master control software with good signal strength. You can connect the device by re-downloading the trouble one. please give me some advice~

[Ole Bauck]

So after you re-downloaded, the problem went away? This is probably because you erased bond information in the flash. Some SDK examples will do advertising with whitelist if there is stored bond information. If the device advertise with whitelist, no other device other than the devices in the whitelist can connect.