If you use Microsoft OneDrive and have Mojave installed, OneDrive sync is corrupting your SSD because it doesn't appear to handle APFS correctly. The only current solution is to uninstall OneDrive and remove the OneDrive folder, as Disk Utility cannot fix the corruption. Deleting the OneDrive folder seems to eliminate the problem in most cases, though some people have had to restore from Backup.
MS is blaming Apple, but given this problem doesn't exist with GoogleDrive or DropBox, I'd say MS is wrong, but I can't prove that.
https://answers.microsoft.com/en-us/msoffice/forum/msoffice_onedrivefb-mso_mac-mso_o365b/disk-utility-warnings-in-os-x-mojave-and-onedrive/3e421ae5-45f4-44c4-acb2-021a3814279b
I've done a bunch of testing and found that as soon as OneDrive sync is turned on, the corruption occurs. Removing the folder fixed the problem for me. YMMV.