Super close range mob leashing in Burning Woods
 

Friend was swarming in burning woods, noticed some really weird things. Mobs will completely de agro after a set period of time, even super close range. Video posted to show this happening. https://www.youtube.com/watch?v=X3G9yFgvKcE
Timestamps- 21 seconds first skeleton de agro, I target him showing 100% hp (not low hp runner)
56 seconds two mobs de agro, one actually agros my character which was not on its agro list previously
1:12 at this point many mobs start de agroing.
New custom EQ feature? This has happened many pulls, not a one time occurrence

I think what's happening is the Bard is pulling more than 25 mobs into his swarm. Which means that only 25 of those mobs take damage while the rest are not getting hit by the bards aoe songs. If you don't do any damage to a mob after a certain amount of time, I'm not exactly sure what amount this is, they will lose aggro and reset their hate tables. That's why they were walking away. They only aggroed you because they no longer had the bard on hate table and you were within aggro range when they reset. Those mobs are KOS, so they will aggro anyone in range. This has been on P99 for quite awhile. For at least as long as I have played, about 5-6 years now.
As to whether or not this is a classic feature, I have no idea, but I believe it has been this way for awhile.

While this is an interesting idea I believe it is incorrect as before this video starts I had 20+ mobs decide to leave at the exact same time and these are mobs that were pulled over a 10+ minute timeframe. It would be nice to figure out what causes this though