I had to reinstall Z3TA+ 2 when I loaded the VST3 version for the first time in Live 10 on macOS 10.12 in order to trigger the online activation again. Nothing changed otherwise on the machine. I'm not sure there was a new activation, because I had to add the AU version (that had the serial all the time) to my project once more, before the serial showed up in the VST3 version next time I loaded that. I assume there was activation though. Flaky, but got it working. Phew! Happy every time I can continue to use this gem of an instrument.