It still works as intended most of the time but sometimes it can completely fail, I've seen it fail around 4 or 5 times now, it works intermittently (since one or two updates ago).

The bug usually occurs when there are a sequence of AI ranged attacks on a belivent wizard, the wizard will often successfully dodge the first ranged attack but then die to the second or third ranged attack (rather than evade every single ranged attack 100% of the time, as intended). It might be an issue with the way AI attacks are sequenced.

If you could post a short video (e.g., from playback) or a series of screencaps the next time this happens, that'd be great.
Belivent will not retreat to a position that puts the victim adjacent to an enemy creature.
If this is what is happening, a change to the talisman description is perhaps the fix.

CGR wrote:Belivent will not retreat to a position that puts the victim adjacent to an enemy creature.

Yes I think that is what is happening, I do have a video showing exactly this (I'll edit/clip/post it later).

Is this a new rule? I'm sure the wizard used to just get thrown around like a pinball regardless of how many enemies were surrounding him.

It's always been this way. Belivent uses the old retreat code back from when stuff could retreat from combat.