This is a Minecraft NeoForge 1.21.1 server hosted on a home network.
Every 5 minutes there is a big lag spike when the world save happens. Players can still walk around but blocks you place or break can snap back after. You also cannot open inventories during the spike.
The freeze only lasts about 5 seconds but it keeps happening and it gets annoying during fights. The owner is trying to change the save timing to something like 15 minutes or disable it and run saves with scheduled commands. They already tried save off and it did not stop the spikes. They also tested mods and one made the spike shorter but did not fix it fully.
