Yes this happened to me today before the dive like last night everything worked ok but mid way through the dive I realised I was in free and now I am locked out of EAN/AIR and the no fly symbol is up and the dive alarm tiny little symbol is also up so guess I will have to wait and see how it goes after 48hrs or so, surely there must be a reset proceedure!!!!
If it's a recent enough model, it probably has a "supercapacitor" to keep the memory going during battery changes. Those things do have a limited runtime, but you never know how big/long.