Here is some more update on the issue. I have exactly figured out what's happening.
Let say there are two situations A and B.
In A, a monster gets normal stunned first and then get mega stunned. Then comes the affected enemy's FIRST turn arter being affected.
In B, a monster gets mega stunned first and then get normal stunned. Then comes the affected enemy's FIRST turn arter being affected.
Now the bug i mentioned only happens in situation B.
Because of your update that says new stuns can't put on old until the affected monster get a recently stunned.
But this shouldn't happen. We would want mega stun to prevail. Otherwise our monster with mega stun skills now become more and more useless. I think this is possible in freeze scenario too. I haven't tried it yet. Let's say xiron the ruby. She now become totally useless crap...... Already you have released tons of ruby counter monsters and now these things make ruby more useless. Why the heck we all spend our money on ruby? You guys keep degrading the product after selling it. Same is with the relics that are triggered by stun or freeze. There is no relic that is triggered by mega stun/freeze. But didn't you guys said, "we want to unify stuff". Then make stun and freeze relic being triggered by Mega and normal stun/freeze. Because now that mega traits give recently thing, there are higher chances of monsters getting recently stun/freeze. That means lesser chance for new stun/freeze. That means less chance for a dependent relic to trigger. There are already very low chance of such relic getting triggered. Niw the chances are being decreased more.