I have the same issue with just the clock setting only at __-__, this winter when the temp reached -20 to -30 and and is been at that state when i start every time, there is a cold snap where i am this week.
I will call the service to inquire if this is common.
I had my X5 for a year now and this has happened once or twice in the past even on normal temperatures.
anyone out there could share a solution would be appreciated

I previously posted about the clock reset issue. but ended up with the E53 forum
IT happent to me again and gave me a warning message and I think this could be the source of the the lock reseting.
I starting that there was a battery surge and I think it is because I was using a few accessories at the same time. front seats heating (2), steering wheel heat and probable radio and lights before completely turning off the vehicle, maybe because shuting ift of after a minute when I got off the X5 and locking it to shut off.
I have tried to use less or shutting them down before I turn off the engine and I have not replicate so far.
I hope this would be a good tip but I still think that BMW should address this matter.