Was running into this issue myself and this was helpful! After some digging around on the Apple forums I also discovered that library validation is only available for macOS 10.9 and up. I was able to get my AUs to run in ARM mode by including the Runtime Exception you suggested, but changing the OS target to 10.9 or higher also fixed the problem without needing that exception.
Im wondering now why this is only an issue with the ARM builds, if library validation doesn’t work when you target 10.8 why isn’t that an issue for Intel builds? Seems like we might keep discovering some back compatibility quirks with these Universal Binaries for a while.