I've installed the unofficial CM11 ROM by u-ra (many thanks) and it's working very well apart from a couple of minor sound related issues that I've not tested fully enough to confirm - (there seems to be a lot of echo for the caller when on speaker phone, and there's some distortion at the higher volume settings).
The reason I'm posting though is that I've found an app and action that reliably causes the phone to crash. It's the BBC iPlayer app - if I start playing any video the phone starts making a single loud tone for a while then crashes. Playing audio only with the partner BBC iPlayer Radio app works without issue.
I've attached the output from /proc/last_kmsg
Thanks again for getting CM on the mini 2 - it's a breath of fresh air after all that cruft that came with the stock phone.