Thanks for raising this. I had a go with 5.4.7 and saw the same behaviour, so I don’t think this has changed recently, if at all. I’ve added some jassert checks which should help to prevent this sort of issue in the future, although of course this will only have an effect when running a JUCE AAX plugin under a debugger. I’ll update this post once the changes are on develop.
I noticed that the AAX SDK already has some built-in assertions that warn about truncated param IDs. To view these assertions, you can search for AAX_ASSERT in the Pro Tools log files. On my copy of Pro Tools 2020.9, I had to enable log output in “Setup → Preferences… → Operation → Save Logs…”, and I could then view the logging output in /Applications/Logs. It’s probably a good idea to get into the habit of scanning these log files periodically when testing AAX plugins, as they can provide useful diagnostic output without needing to attach a debugger.