Anyone feel like it doesn't work as it should sometimes? I'm not sure how they programmed it to terminate but I feel like if I even move to a different command while stuck in a combo I die.

Once more is disabled whenever you use a command, as far as I can tell.

I'm not using the command. Just getting ready to use cure.I've seemed to have died to the same attack without doing anything though. So I'm curious as to why certain moves bypass it.

Differences in the definition of a combo, probably. Maybe some attacks don't count as a combo for Once More, but you still can't use commands between them.

Some moves that have a certain hitstun bypass it.

 

Sometimes enemies hit me and reduce me to 1 HP, and before I can heal myself they hit me again, and it bypasses Once More. Presumably that means you cannot use commands yet, but can do other things like dodge. In that situation, you'd have to dodge, then heal, or risk being killed.

Some you can't get out of like

Ansem Form I's barrier dash