I have this exact same problem, and it's not working as it should be. Instead of progressing +1, +2,... it's progressing +2, +3...
There is an extra +1 that shouldn't be there.
I've also had the problem with 3 combat rolls for the Skinsaw Man.
The extra middle roll seems to add my previous combat roll to the difficulty.
First time i encountered the error I got +17 after rolling 17 on the first check and then he did a third check that behaved as the second check should
Second time I encountered the error I got +8 after rolling 8 on the first check and then again he proceeded to a third check that behaved as the second should.
Once he behaved just as he should.
All three times it was my first time in the scenarion to encounter him, so I had the little conversation cutscene. The two times I got the extra third check he rolled his solo bonus d4 during the cut scene, the time he didn't bug out he rolled it before. Both times he bugged out I was at the Warrens and the simultaneous cutscene/die roll happened after the adding of a random monster to another location.
Fourth time I tried the scenario, he automatically rolled my combat dice after leaving the cutscene. Then I got fed up...
All these bugs were encountered in a Sajan solo run if that matters.