so, for the LONGEST time, this was, in fact, the perfect set for openemu (2013-12-20 - 2019-11-13 (almost 6 years!)), but openemu starting updating the underlying ume core to more closely match the official mame releases. you can see more of this, here:
https://github.com/OpenEmu/UME-Core/releases
the latest (as of this writing) openemu ume (mame) core is 0.235; the latest official mame release is 0.239.
since the 2019 openemu update, there have been 6 underlying ume updates REQUIRING matching mame sets (and even within there, there have been some screwy folder organization changes). so, you have two options:
• stay up-to-date hovering between openemu and official (which are often close, if not overlap), or
• LOCK your ume core: go to ~/Library/Application Support/OpenEmu/Cores, and then get info on and click the "lock" checkbox for UM
E.oecoreplugin. bonus points if you download the release you need from the above link and replace the core before locking.