automation - Systemd unit file only works for one instance name, not the other

There are two Minecraft servers running on my Debian server. In order to avoid all the busywork of manually coordinating multiple tmux sessions, I wrote a systemd unit file to do all of that for me:

[Unit]
Description=Minecraft Server: %i
After=network.target

[Service]
WorkingDirectory=/opt/minecraft/servers/%i
User=minecraft
Group=minecraft
Type=forking
RemainAfterExit=yes

#Restart=on-abnormal

ExecStart=/usr/bin/tmux new -s mc-%i -d '/usr/bin/java -Xms1G -Xmx4G -jar forge-universal.jar nogui'

ExecStop=/usr/bin/tmux send -t mc-%i 'say SERVER WILL SHUT DOWN IN 10 SECONDS' ENTER
ExecStop=/bin/sleep 10
ExecStop=/usr/bin/tmux send -t mc-%i 'stop' ENTER

[Install]
WantedBy=multi-user.target

There are two subdirectories in /opt/minecraft/servers/: private and otherserver. These directories' file listings look like this:

minecraft@server ~ # ls -la /opt/minecraft/servers/private/
total 39180
drwxr-xr-x  9 minecraft minecraft     4096 Dec 20 21:34 .
drwxr-xr-x  5 minecraft minecraft     4096 Dec 19 21:11 ..
-rw-r--r--  1 minecraft minecraft        2 Dec 20 21:33 banned-ips.json
-rw-r--r--  1 minecraft minecraft        2 Dec 20 21:33 banned-players.json
drwxr-xr-x 10 minecraft minecraft     4096 Oct 11 16:22 config
drwxr-xr-x  2 minecraft minecraft     4096 Oct 11 16:11 crash-reports
-rw-r--r--  1 minecraft minecraft      181 Oct 11 16:11 eula.txt
-rw-r--r--  1 minecraft minecraft  4888981 Oct 11 16:10 forge-1.12.2-14.23.5.2768-universal.jar
lrwxrwxrwx  1 minecraft minecraft       39 Oct 11 11:41 forge-universal.jar -> forge-1.12.2-14.23.5.2768-universal.jar
drwxr-xr-x  3 minecraft minecraft     4096 Apr 14  2018 journeymap
drwxr-xr-x  8 minecraft minecraft     4096 Apr 14  2018 libraries
drwxr-xr-x  2 minecraft minecraft     4096 Dec 20 21:32 logs
-rw-r--r--  1 minecraft minecraft      369 Oct 11 15:04 mapcrafter.conf
-rw-r--r--  1 minecraft minecraft 30222121 Oct 11 16:10 minecraft_server.1.12.2.jar
drwxr-xr-x  3 minecraft minecraft     4096 Oct 11 16:21 mods
-rw-r--r--  1 minecraft minecraft      271 Dec 20 21:33 ops.json
-rw-r--r--  1 minecraft minecraft      843 Dec 20 21:33 server.properties
-rw-r--r--  1 minecraft minecraft      322 Dec 20 21:32 usercache.json
-rw-r--r--  1 minecraft minecraft      112 Oct 13 23:18 usernamecache.json
-rw-r--r--  1 minecraft minecraft      171 Dec 18 22:07 whitelist.json
drwxr-xr-x 11 minecraft minecraft     4096 Dec 20 21:33 world

Executing systemctl start minecraft@otherserver results in a new tmux session for the user minecraft called mc-otherserver and a successfully started Minecraft server.

Executing systemctl start minecraft@private, on the other hand, does literally nothing. The command returns instantly, does not spawn a new tmux session, doesn't start a new Minecraft server, nothing. I checked whether the Minecraft instance was just crashing, but it's not that. Manually executing tmux new -s mc-private -d 'java -Xms1G -Xmx4G -jar forge-universal.jar nogui in the server's directory works flawlessly and starts the Minecraft server in a new tmux instance, as intended.

Curiously enough, both servers worked just a few days ago. I checked the changelogs for systemd and tmux, but as far as I can tell, they haven't actually been updated for Debian stable for some weeks.

Additionally, journalctl contains no information about my failing unit file at all, so I'm at a loss here. Does anyone know what could be causing this?

Answer

Sigh. Turns out the minecraft@private service was listed as loaded failed failed in systemctl list-units, and was thus prevented from being started again.

Doing systemctl reset-failed fixed my problem.