5 warnings, 3 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
What this error means, and every way to fix it →
This log contains 62 lines logged at ERROR level. Roastd checked them against its failure signatures and none matched, so they are classified as benign. A plain count of ERROR lines will always be higher than the number of findings here.
The tick loop fell 2025ms behind, 40 ticks in one go
A tick took far longer than the 50ms it is allowed, so the server ran behind real time and skipped ahead to catch up (once in this log). Players see rubber-banding, delayed block breaks and mobs that stutter. One burst after a restart, a world upgrade or a chunk pre-generation run is normal. A steady stream is lag with a cause: profile it with spark ("spark profiler --timeout 120" in the console) rather than guessing. The usual culprits are view-distance and simulation-distance set too high, entity or item build-ups, chunks generating live as players explore, and garbage collection pauses when the heap is too small.
Hosting with the headroom to keep up →Why this happens: Diagnosing server lag →jump to line 1680No 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 4Refmap warnings are cluttering the log
A "reference map could not be read" warning on its own is usually harmless build noise from a mod, not the cause of a crash. Ignore these lines unless a real mixin failure appears further down. They only matter when paired with an injection error.
jump to line 378sync-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 5744 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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