Particularly the river call efficiency stat. Apparently RCE has been calculated incorrectly since HM1 (see my posts in the small stakes stars regs thread if you're interested in the details, I can clarify ITT if people want) such that RCE=1 does not actually imply breakeven river calls. In fact the breakeven RCE depends on opponent betsize, and is somewhere around 0.7 for river sizes people use in today's games.

I posted this to the HM2 forums and got this reply:
So basically because it's always been wrong it's going to stay wrong for now at least.

Consider me interested in the details... Glad to know I'm not as much of a station as I thought? :P

Assume pot is P and your opponent bets B. If you call and lose, RCE=0. If you call and win HM2 calculates RCE as:

RCE = (P+B)/B

So if your opponent bets pot, then RCE=(1+1)/1=2

Now assume this happens 3 times. One time you call and win and twice you call and lose. You win 1+1=2 the time you call and win, and lose 1 the two times you call and lose. So net you breakeven, and one would assume RCE=1 for the 3 hands. But...

RCE = (2+0+0)/3=0.666 (RCE is 2 the time you win, 0 the two times you lose)

The correct calculation for RCE is:
RCE=(P+2B)/B
For a pot sized bet where you call and win, RCE=(1+2)/1=3

The result is instead of a breakeven RCE being 1, as calculated currently by HM2 it actually depends on villain's betsize. Here are some breakeven RCE's for various betsizes:

1/2 pot - 0.75
3/4 pot - 0.7
1 pot - 0.666
1.5 pot - 0.625
2x pot - 0.6

So for today's games, it's going to probably be somewhere around 0.7 as the breakeven value. If they just made the very small change in the formula, then it would work exactly as it should and RCE=1 would imply you're breakeven on your river calls.

I think they definitely should change it to the correct formula even if people are used to the values it provides ATM. That's because everywere I found information about this stat people think that the breakeven point is 1 which is not true.

I agree! But based on the (lack of) responses to my thread, it would appear I am in the minority

I have also posted in your thread in the HM forums but after I read all their responses I'm not very optimistic. Maybe one day... who knows ?

I think it's best for my sanity to not reread that thread :/