Minecraft Server Freezes When a Player Joins

Direct answer

Correlate the freeze with the first relevant stack trace or profiler result instead of deleting the player immediately.

Join-time freezes often point to player data, chunk loading/generation, login plugins, or a mod/plugin reacting to join events.

Provide the join time, username and whether a loading screen stays frozen or the server becomes unresponsive for everyone.
If possible, test with another ordinary account to see whether it follows a single profile or any player entering an area.
Do not repeatedly rejoin a server that is writing a damaged world or player file.

Capture the server log and a safe diagnostic sample while the freeze occurs; check whether MSPT jumps, a player-load plugin blocks, or a watchdog fires.
If only one UUID triggers it, back up playerdata and inspect per-player plugins, inventory contents and last location on a staging copy.
If everyone triggers it, inspect login-time databases, permissions, authentication bridges, joins/teleports and spawn chunk loading.
Temporarily isolate a suspected join listener or database integration in staging; never delete live playerdata as the first fix.

Verify the result: Test the originally affected account and another test account, watching MSPT, login delay and data persistence after the fix.

More allocated RAM does not make a slow main-thread workload faster. Change heap size only when memory/GC evidence supports it.

Use the documentation for the exact software and release you run. These sources support the settings or diagnostic behavior used in this fix.

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