A lot of it has to do with Steam's ♥♥♥♥♥♥ cloud save system if you converted to cloud save that is.

Saving process for large Steam Cloud world save files causes longer stuttering during world saving compared to saving process for Local saves. Simplified, if Player uses Local saves, during saving process, valheim.exe will simply rename worldname.db to worldname.db.old, and then create new worldname.db file which gets filled with newest data from RAM. However, if Player uses Steam Cloud saves, saving process is being done by steam.exe, which due to its API security related restrictions, can't simply rename files. and has to copy entire contents of one file into another. This causes additional stuttering. Check example of stuttering during Cloud saving as opposed to stuttering during Local saving.

When playing using Steam Cloud saves, saving process can last longer, if Windows starts running background transfers at the same time (e.g. windows updates). This can cause Valheim.exe to be unresponsive for longer period of time while waiting for Steam.exe to finish saving. During this unresponsive phase, Player might think Valheim froze, so they might be compelled to close the program or cause it to crash by manipulating the window, which usually results in corrupt