I’ve performed some additional testing. In short, I was able to reproduce the issue you’re currently seeing (401 responses to localhost requests when using the TMDB agent). I was able to correct it by downgrading to PMS version 1.41.6.9685.
There was another thread recently regarding a regression in plug-in behavior (failure) on 1.41.7.9817. I can’t find the thread now, but I’m pretty sure it was found and will be corrected in the next beta. I believe these issues are related since the legacy agents are plug-ins.
It still doesn’t explain why the modern agents are working for some folks, but downgrading to the last “stable” release should allow the use of legacy agents at least.
Is this (downgrading to 1.41.6.9685) something you can confirm on your side? To see if it “fixes” the legacy agents?
[Edit]
Here’s the thread I referred to above:
