I also encountered this bug and tried some more advanced ways to get some info.

The best way to reproduce it was

    while true ; do mkdir abc ; sleep 1 ; rmdir abc ; sleep 1 ; done

the extra conditions are:
- Details mode
- Split View
- the directory is on the separate partition (also called /media/data :) )
- when it's reference by symlink

The conditions are not necessary, though; I saw it also on files and on non-symlinked directory.

Also I noted that it's possible to play with KDirWatch's preferred method using the environment variable, KDIRWATCH_METHOD. Of the four methods available (Fam, inotify, QFSWatch, Stat), I could reproduce the bug only on inotify.

Also I was trying to get some more advanced info to detect whether something is wrong with interpreting inotify's data. To do this, I set s_verboseDebug to true in kdirwatch.cpp.

I got the following in the log after creating/deleting directory "abc":
kf5.kcoreaddons.kdirwatch: path= "/media/data/Tasks/ptz2020/day4" sub_entry: 0x0
kf5.kcoreaddons.kdirwatch: path= "/media/data/Tasks/ptz2020/day2" sub_entry: 0x0
kf5.kcoreaddons.kdirwatch: path= "/media/data/Tasks/ptz2020/trial" sub_entry: 0x0
kf5.kcoreaddons.kdirwatch: path= "/media/data/Tasks/ptz2020/day1" sub_entry: 0x0
kf5.kcoreaddons.kdirwatch: path= "/media/data/Tasks/ptz2020/day3" sub_entry: 0x0
kf5.kcoreaddons.kdirwatch: Added Dir "/media/data/Tasks/ptz2020/abc" for "" ["KDirWatch-6"]
kf5.kcoreaddons.kdirwatch: inotify successfully used for monitoring "/media/data/Tasks/ptz2020/abc" wd= 82
kf5.kcoreaddons.kdirwatch: Added already watched Entry "/media/data/Tasks/ptz2020/abc" (now 2 clients) "[KDirWatch-4]"
kf5.kcoreaddons.kdirwatch: Added already watched Entry "/media/data/Tasks/ptz2020/day1" (now 2 clients) "[KDirWatch-4]"
kf5.kcoreaddons.kdirwatch: Added already watched Entry "/media/data/Tasks/ptz2020/day2" (now 2 clients) "[KDirWatch-4]"
kf5.kcoreaddons.kdirwatch: Added already watched Entry "/media/data/Tasks/ptz2020/day3" (now 2 clients) "[KDirWatch-4]"
kf5.kcoreaddons.kdirwatch: Added already watched Entry "/media/data/Tasks/ptz2020/day4" (now 2 clients) "[KDirWatch-4]"
kf5.kcoreaddons.kdirwatch: Added already watched Entry "/media/data/Tasks/ptz2020/trial" (now 2 clients) "[KDirWatch-4]"
kf5.kcoreaddons.kdirwatch: got event 0x400 for "/media/data/Tasks/ptz2020/abc"
kf5.kcoreaddons.kdirwatch: -->got deleteself signal for "/media/data/Tasks/ptz2020/abc"
kf5.kcoreaddons.kdirwatch: 4 "/media/data/Tasks/ptz2020/abc" 2 clients
kf5.kcoreaddons.kdirwatch: Added already watched Entry "/media/data/Tasks/ptz2020" (for "/media/data/Tasks/ptz2020/abc" )
kf5.kcoreaddons.kdirwatch: "KDirWatch-6" emitting deleted "/media/data/Tasks/ptz2020/abc"
kf5.kcoreaddons.kdirwatch: "KDirWatch-4" emitting deleted "/media/data/Tasks/ptz2020/abc"
kf5.kcoreaddons.kdirwatch: 
kf5.kcoreaddons.kdirwatch: scanEntry for "/home/gepardo/.local/share/user-places.xbel" says 0
kf5.kcoreaddons.kdirwatch: "/media/data/Tasks/ptz2020" e->m_ctime= 1580594624 01:03:44 stat_buf.st_ctime= 1580594669 stat_buf.st_mtime= 1580594669 e->m_nlink= 1 stat_buf.st_nlink= 1 e->m_ino= 437305 stat_buf.st_ino= 437305
kf5.kcoreaddons.kdirwatch: scanEntry for "/media/data/Tasks/ptz2020" says 1
kf5.kcoreaddons.kdirwatch: 1 "/media/data/Tasks/ptz2020" 1 clients
kf5.kcoreaddons.kdirwatch: scanEntry for "/media/data/Tasks/ptz2020/abc" says 0
kf5.kcoreaddons.kdirwatch: scanEntry for "/media/data/Tasks/ptz2020/day1" says 0
kf5.kcoreaddons.kdirwatch: scanEntry for "/media/data/Tasks/ptz2020/day2" says 0
kf5.kcoreaddons.kdirwatch: scanEntry for "/media/data/Tasks/ptz2020/day3" says 0
kf5.kcoreaddons.kdirwatch: scanEntry for "/media/data/Tasks/ptz2020/day4" says 0
kf5.kcoreaddons.kdirwatch: scanEntry for "/media/data/Tasks/ptz2020/trial" says 0
kf5.kcoreaddons.kdirwatch: path= "/media/data/Tasks/ptz2020/abc" sub_entry: 0x0
kf5.kcoreaddons.kdirwatch: path= "/media/data/Tasks/ptz2020/abc" sub_entry: 0x0
kf5.kcoreaddons.kdirwatch: path= "/media/data/Tasks/ptz2020" sub_entry: 0x5622d961b920
kf5.kcoreaddons.kdirwatch: Removed Dir "/media/data/Tasks/ptz2020/abc" for "" ["KDirWatch-4"]

During the next creation/deletion rounds, no log entries appeared.

I hope this information can be helpful while finding the bug, and I'll try to dig more of it.