1. List available local snapshots

First of all, you need to find out how many local snapshots exist in your local SSD. To do so, you need to execute the following command:

sudo tmutil listlocalsnapshots /Volumes/

2. Delete local snapshots

Next, you need to manually delete each local snapshot based in there <snapshot_date>.

sudo tmutil deletelocalsnapshots 2017-10-20-002004