I've loaded my pre-fight save a couple more times and it definitely seems to be rigged with the same miss chance. Round 2 does not seem to always be the same.
But I disagree: the system is not flawed because of a calculation problem.
The system is flawed because it exists in the first place!!!
I don't care what other, completely unrelated games in different genres created by different developers do. This is not Fire Emblem. I am talking about D:OS 2. This is VERY BAD DESIGN.
Allowing free use of save scumming to get different results in combat is far, far better an idea than this terrible garbage deciding in advance, before a fight even BEGINS whether or not your attack on an enemy will hit.
It is INDEFENSIBLE. PERIOD.
