Thank you for your reply!
We've tested a bit more, and I have to admit, the description I gave was a bit overly simplistic (I've included the details now in the full description.
To be precise, skeletons start to have random behavior and don't flee anymore at around Y 140 in the nether. We've made a video to show the bug more precisely.
EDIT: We've just found out that this is not only true in the nether, but also in the overworld on Y 140+ Coordinates
Confirmed in 1.11.2.
Happening on a vanilla pc server 1.11.2 with minecarts. I have removed all minecarts and minecart items from loaded chunks. The warning messages still appear.
Can I get this reopened please. The mods response is not a response.
Development console as above when attempting to launch minecraft
Not a mod, but as far as I know, it is because the second item gets burned by the lava. When two items are dropped, one is collected instantly while the other is laying for a short amount of time on the ground, enough for it to be burned by the lava. I remember ilmango explaining this occurrence in his videos once (panda slime farm in the peaceful series, iirc).