Yes, undo is very limited - especially when it comes to batch edits, unfortunately. There don’t seem to be any workarounds. I don’t know if metadata is the reason, but there is a lively discussion of the problem here:
You can vote and comment there to request that DxO improve the undo capabilities.
I don’t recall seeing any clarifications by DxO (yet) about the problem or what their plans are to address it.