nrf52 "pairing took too long" with iPad - HID keyboard device

[MattFL]

Please point me in the right direction if you can, I'm stumped.  My project is based on the app_hids_keyboard sample, using the pca10040 board (nrf52832) and SDK 14.2, soft device s132.  It pairs great with Android devices, and some iOS devices. But on my customers iPad he frequently gets "Pairing Unsuccessful Pairing took too long".  After enough fiddling it will eventually connect, but he gets this error more often than not.  I'm told he is using the latest iOS and that it's an iPad mini 4 running iOS 11.3.1 (the latest).  Are there any known issues between the Nordic and Apple devices?  

Edit --> I reproduced the issue here with an older iPad.  What is actually happening is the Nordic device will not re-connect to iOS unless the bonds are cleared.  If the bonds are cleared, iOS reconnects almost instantly.  But without clearing the bonds, iOS won't reconnect reliably.  Does this ring bells to anyone? 

[run_ar]

My initial thought is there could be a mismatch between advertsiment address and the actual address in case directed advertising is used. Or that there could be a whitelist that is missing the irk for the iOS device. Do you have a sniffer trace that shows the first succesfull bond and later on the failed reconnect?

[MattFL]

Thank you for the reply.  The pairing code is directly from your app_hids_keyboard example without changes.  I don't have a sniffer at the moment, I will try to convince my boss will spring for a nRF51 dongle so I can use your sniffer software. In the meantime any tips you could provide would be great.