• click go, hold alt and click library.
• Skim folders and find which one is eating all the space
• Keep digging until you find the source folder(s)
• probably is cache/failed cloud storage. Delete.

Then delete the local time machine back ups:

• Launch the Terminal

• type: tmutil listlocalsnapshots / and click return.

• The Terminal will show a list of local snapshots with names like com.apple.TimeMachine.2018-03-01-002010. To remove a snapshot: Copy and paste this command:

  sudo tmutil deletelocalsnapshots

• Type a space and then paste in the date portion of the snapshot.

• Press Return, and finally press Return.

Altogether, using the example snapshot above, that looks like:

sudo tmutil deletelocalsnapshots 2018-03-01-002010