Hi EagleEye,
Thanks for your message, and welcome to deSEC! 
The most likely cause is that for some reason, your device is sending an update request at some point with an empty IP parameter, which causes the record to be deleted.
If this happens again, please contact support a day or two later (we don’t keep logs very long), and let us know about the date and the domain name in question. We can then look into what caused this.
Hope that helps!
Stay secure,
Peter