com.apple.xpc.launchd & com.apple.mdworker.bundles pollute logs with errors

I see, Dustmoo.. I thought the issue was caused by having that account with UID 502 in my main partition. So I dug it a bit more using your example. I actually couldn't find any mdworkers directory in /var. So I looked for the files owned by UID 502 (but it could be any other UID. One must check the last number in the error message, the one I underlined in my first post and use it instead of 502 in the following code):

cd /var

sudo find . -user 502 -exec ls -ld {} \;

This has been the output:

drwx------ 5 michele _spotlight 170 Oct 16 19:10 ./folders/zz/zyxvpxvq6csfxvn_n0000000000000/0/com.apple.Spotlight/502

drwx------ 2 michele _spotlight 68 Oct 16 19:10 ./folders/zz/zyxvpxvq6csfxvn_n0000000000000/0/com.apple.Spotlight/502/0

drwx------ 2 michele _spotlight 68 Oct 16 19:10 ./folders/zz/zyxvpxvq6csfxvn_n0000000000000/0/com.apple.Spotlight/502/C

drwx------ 2 michele _spotlight 68 Oct 16 19:10 ./folders/zz/zyxvpxvq6csfxvn_n0000000000000/0/com.apple.Spotlight/502/T

(michele is my username for UID 502)

So it was still in the /var/folder directory, but something related to or created by Spotlight one week ago. Not sure how it went there, since this was a fresh installation in that partition. It really looks like junk to me.

Just in case I removed the incriminated directory:

cd /private/var/folders/zz/

# I did some directory listing and other things just to check

sudo rm -r zyxvpxvq6csfxvn_n0000000000000

And rebooted. I can't really say if it changed anything because I had already made the new account, but it does look like the culprit.