@Robert Bowles, @Marc Larue
Download the original "1.14.4.json" file and the 1.14.4 Client here: https://minecraft.gamepedia.com/Java_Edition_1.14.4 then reformat it.
It appears that this issue is caused by "1.14.4.json" file formating being broken and obfuscation maps entries now being included in the 1.14.4.json file.
Reformating the "1.14.4.json" file with a json editor and removing the obfuscation maps entries then adding this fixed json as a custom version seems to fix it.
Update to the new launcher.