The 11GB of lost space cannot be blamed on two days of logs alone or on a few emails that have no large attachments. You have to consider either a host of activities or some fault in the system. Let’s start with the host of activities to consider….
– Torrent downloads. If you don’t use any torrent client app, forget about this one. If you use any torrent client, know that it can automatically download files any time it is open and the system is online.
– Email. If you have your email client set to save all messages, that can cause a lot of space to be lost after several emails with large attachments.
Logs. These typically on gain a few megabytes in two days, so unless you are doing a million tasks each day, forget about this one.
– iOS device backups. Well, you should know if you have been connecting any iOS device for backup, so this is an unlikely cause.
– Hidden sleepimage and swapfiles. When the startup disk gets nearly full, the size of the sleepimage and swapfiles shrinks drastically to allow the system to keep running while you make a backup and trash >>15%<< or more of the total storage size. For a 256GB storage, you need to get rid of at least 38GB of stuff. If you only get rid of 20GB of stuff, the sleepimage and swapfiles will grow during normal use of the system. They grow, because the system recovers from sleep faster and completes complex tasks faster when those files are large. The size of the sleepimage file is related to your data open when the system goes into sleep mode. The size and number of the swapfile(s) is related to your tasks that exceed the total memory (RAM). To investigate if this can be the cause, check the size of the hidden directory that contains these files….
– In a Finder window, press command shift G.
and then press Return (or click “Go”).
– Select the vm directory, and press command I (or go to the menu bar, File > Get Info).
Note that it isn’t an advantage to have large swapfiles, but it is often necessary. With more RAM, the system will not need to generate many swapfiles.
As to some fault in the system, the most likely would be corrupt .DS_Store files. To get rid of the HUNDREDS of .DS_Store files (new, clean ones will regenerate automatically), download and run the app at the link below. The system will be slow for viewing files for some time after those files are deleted, since their purpose is similar to cache.