It turned out there was another sub-task, TS Y - same software installation but was placed under different step in TS B only and there were no Continue on error set.
Sub Task Sequence changes do not apply
We have serious problem during the production, where we use 2 different main TS;
TS A - Apply OS A
TS B - Apply OS B
TS X - Sub TS added to A and B with Install Software X, Y, Z,
Now, we know that Software X might fail, so we use continue on error.
Situation is, that Continue on Error works on TS A, but not TS B. TS B does not inherit any changes from TS X. Is this a bug?
I have already tried redeployng TS A and B, set Software X to disable, but no. Our TS A works, TS B fails because software X fails.