This is a daily occurrence for me as well. Same remedy. I’ve had the same issue over many updates.
I disconnected all but one network interface and rebooted. Rebooted the Qnap.
Still doesn’t work, it still gives the same error.
I tried reinstalling Plex, and it still gives the same error.
I tried accessing Plex through the https:// and http: methods listed above.
https://192.168.0.43:32400/web
Or
http://192.168.0.43:32400/web
Results in the following error:
Not Found
The requested URL was not found on this server.
Any new ideas?
I gave up on this app, instead I installed Ubuntu lxc in docker container installed Plex server that connects to a own network adapter, vpn as second one and finally now everything works as expected.
Then we need to use SSH 
See Qnap faq.....read me first! Q13
When in a console, type:
$(getcfg -f /etc/config/qpkg.conf PlexMediaServer Install_path)/plex.sh restart
Then show us what it says
My plex server on QNAP is in a condition where it will start, complain that the library database is locked and then crash, can anybody from plex take a look at these logs? Seems similar to OP but the server only stays up for a couple minutes then crashes. This has happened twice now, had to rebuild the libraries the last time this happened.
Restored library DB (includes removing .shm and .wal files) - FAIL
Restored files, reboot NAS - FAIL
Plex UI tools - FAIL
Equipment:
Qnap: TS-451+
QNAP Ver: 4.5.4.1741
Plex ver 1.23.4
Plex Media Server Logs_2022-01-10_16-01-31.zip (1.4 MB)
i ran the command in putty:
$(getcfg -f /etc/config/qpkg.conf PlexMediaServer Install_path)/plex.sh restart
Plex Media Server hasn’t been enabled or started…
Starting Plex Media Server…
[~] # Error: Unable to set up server: listen: Address in use (N5boost10wrapexceptINS_6system12system_errorEEE)
what do we do now?
Restart your QNAP for a fast solution, if not used to SSH console
rebooted the qnap, still having the same issue
Whats next?
Back into SSH
Type:
$(getcfg -f /etc/config/qpkg.conf PlexMediaServer Install_path)/plex.sh stop
ps aux|grep Plex
Show the output
[~] # $(getcfg -f /etc/config/qpkg.conf PlexMediaServer Install_path)/plex.sh st op
Plex Media Server hasn’t been enabled or started…
[~] #
[~] # ps aux|grep Plex
30015 admin 1024 S grep Plex
[~] # $(getcfg -f /etc/config/qpkg.conf PlexMediaServer Install_path)/plex.sh stop ps aux|grep Plex
Plex Media Server hasn’t been enabled or started…
[~] # ps aux|grep Plex
2195 admin 1012 R grep Plex
an
According to above, you should be fine in starting it from QTS AppCenter now
still doesn’t work.
i upgraded plex to the jan 13 release plex version 1.25.3.5409-f11334058
didn‘t fix anything. stopped plex in the app center, and ran the script again.
[~] # $(getcfg -f /etc/config/qpkg.conf PlexMediaServer Install_path)/plex.sh stop
Plex Media Server hasn’t been enabled or started…
[~] # ps aux|grep Plex
30694 admin 984 S grep Plex
[~] #
any other ideas?
The only other idea I have is to completely wipe and reinstall the qNap Nas, but I’d have to purchase a 16TB external drive in order to back up the entire server. That would take a lot of extra time and money.
What happens if you now type
$(getcfg -f /etc/config/qpkg.conf PlexMediaServer Install_path)/plex.sh start
[~] # $(getcfg -f /etc/config/qpkg.conf PlexMediaServer Install_path)/plex.sh stop
Plex Media Server hasn’t been enabled or started…
[~] # $(getcfg -f /etc/config/qpkg.conf PlexMediaServer Install_path)/plex.sh start
Starting Plex Media Server…
[~] # Error: Unable to set up server: listen: Address in use (N5boost10wrapexceptINS_6system12system_errorEEE)
what does this mean?
It means that something is already running on port 32400
In an ssh console, type
netstat -ltnp | grep 32400
Then show me the output
[~] # netstat -ltnp | grep 32400
tcp 0 0 0.0.0.0:32400 0.0.0.0:* LISTEN 21971/myupnpmediasv
Please stop that app, in order to get Plex up and running, unless it can be configured to use another port?
After stopping/changing port, you should be able to start your PMS
And looks like you can change the port of it
Ref: How to enjoy multimedia content stored on the QNAP NAS via DLNA/UPnP? | QNAP
Edit: And the big Q here is: Are you actually using it, or does it simply run and burn CPU cycles?
I reassigned the port to 32401 and stopped the media streaminig addin. I then restarted Plex within the app center.
resulted in the same error
$(getcfg -f /etc/config/qpkg.conf PlexMediaServer Install_path)/plex.sh stop
Plex Media Server hasn’t been enabled or started…
[~] # ps aux|grep Plex
18908 admin 972 S grep Plex
[~] #
