Everything was ok a day ago. Everything ok with another spec. I deleted all saved variables, same result.
That does seem like a relatively straightforward problem: You’re off-hand weapon (Horseman’s Sinister Slicer) does not have Strength but Agility which is useless as a Death Knight. AMR completely ignores weapons with wrong stats because not doing so would exponentially increase the complexity and amount of simulations required and generally speaking you’ll never want to equip such a weapon anyway.
If those are your only two weapons then the optimizer doesn’t really know what to do - you’ll need two weapons but there is only one weapon available.
I used this weapon before, before Spliter drops, and everything was ok.
Yeah… as asashdor said, there are some edge cases that we don’t handle to save some time. This is one of them, where you don’t have enough “appropriate” weapons for your spec (in this case, 1-handers with strength as the primary stat).
Once you get a second 1-hander with strength, everything should be fine (and you’ll do more damage!).