5 warnings, 2 observations found. Every finding below comes from what was actually in the pasted files. Treat the fixes as suggestions: they cover the common causes, and this case may need more digging.
NeoforgeMinecraft 1.21.1Java 21151 mods
This looks like a client log, not a server log. The findings below apply to the player's machine.
What this error means, and every way to fix it →
An unrecognised crash: NullPointerException in Unexpected error
The crash report says it died in Unexpected error. The exception is java.lang.NullPointerException: Cannot invoke "com.drmangotea.tfmg.content.decoration.tanks.steel.SteelTankBlockEntity.getBlockPos()" because the return value of "com.drmangotea.tfmg.content.decoration.tanks.steel.SteelTankBlockEntity.getControllerBE()" is null. The loader suspects Not Enough Crashes (notenoughcrashes), Iris (iris), Minecraft (minecraft), NeoForge (neoforge). Mods with code injected into the frames it crashed on, most involved first: betterf3, ae2wtlib, create, dynamic_fps. That is a bisect order, not a verdict: disable them one at a time and repeat the action that crashed it.
Usual suspects: betterf3; ae2wtlib; create; dynamic_fps.
No tuned GC flags. Every pause is the default kind.
Add Aikar's flags to the startup command (search "Aikar flags generator"). They tune the G1 garbage collector for Minecraft and smooth out tick stalls at zero cost.
Hosting with tuned flags as standard →Why this happens: Allocating more RAM →jump to Specs line 1Auto-restart off. Downtime measured in how long you sleep.
Run the server under a wrapper or service that restarts it on exit (systemd, a start script loop, or a panel that does it for you). A crash should be a blip, not a night offline.
Auto-restart on crash →Default max-tick-time plus mods. The vanilla watchdog does not know what patience is.
Set max-tick-time=-1 in server.properties on modded servers. Heavy worldgen legitimately exceeds 60 seconds, and the watchdog kills the server for it.
Why this happens: Diagnosing server lag →jump to server.properties line 33allow-flight=false with mods installed. Jetpacks are a kickable offence here.
Mods that grant flight trip the vanilla anti-fly kick. Set allow-flight=true on modded servers or players get kicked mid-air.
Why this happens: Kicked for flying →jump to server.properties line 4sync-chunk-writes=true. Every chunk save politely queues behind the disk.
Set sync-chunk-writes=false on vanilla, Forge and Fabric servers for a real performance gain on chunk saving. Paper already handles this for you.
Why this happens: Diagnosing server lag →jump to server.properties line 58spawn-protection=16. New players cannot build at spawn and nobody tells them why.
Non-op players silently cannot place or break blocks within 16 blocks of spawn. Set spawn-protection=0 unless you want that, and op at least one admin.
Why this happens: Diagnosing server lag →jump to server.properties line 5728 sensitive values (addresses, passwords and the like) were stripped before this page was stored.
As received, after redaction.
Problem lines are highlighted.
As received, after redaction.
As received, after redaction.
As received, after redaction.
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