I've investigated Joseph's issue. The problem seems to be in the file naming of the original .lrtemplate file itself. If the original .lrtemplate file name contains any special characters (in this case, it is the forward slash "/" in the .lrtemplate file name). On macOSX, forward slash "/" has special meaning, which is is the folder delimiter.
If you manually change the “/” character in the .lrtemplate file name to a space character, then relaunch Lr and it would convert the preset correctly.
Joseph, I have replied to your email regarding the two specific .lrtemplate file that has the "/" in them. Lr should have handle this kind of exception better. I’m making a fix that better handles and report the issue in Lr.
https://helpx.adobe.com/lightroom/kb/not-all-presets-are-converted.html