I've not update BattleMentat for a while now (will be doing so soon though), so there is no reason for there being any accuracy problems.
Could you please confirm that it isn't an issue with the new large battle algorithm, which is currently effecting x2 conquest where more than 10m units are involved?
If that isn't it, then please send me an espionage report, tech levels, and battle report, so that I can double check.