Yes. After my iPhoneXS upgraded to iOS 12.1.1, my bluetooth connection to the Kestrel was lost.Sorry about all of this. Please try this: try a soft reboot of kestrel, take battery out and hold down the power key for 30 seconds. Then put the battery back in and see if it will connect with the Kestrel Ballistics App. You will need to calibrate the compass before shooting again, but hopefully the new name will register with the ballistic app. Again, let me know the results.
Also, you say your iPhone X operating system upgraded and that was the beginning of this problem?
I downloaded the Kestrel Link to my computer and used the NK Dongle to try to connect my computer to the Kestrel. The connection dropped by itself before I could rename the Kestrel.
I then attached the Kestrel to my computer with the USB Data Transfer cable and was able to rename my Kestrel. This finally allowed me to connect again with the Kestrel Link Ballistics on my phone with the Kestrel by bluetooth. The connection is finally holding.