Strange, large $TMPDIR/Deleting-<UUID> Folders using up disk space

I've noticed that on some of our CI Macs lots of Disk space is being used up by some strange folders in $TMPDIR.

The folders in question are ~3gb and Prefixed with "Deleting-" e.g.

• Deleting-9B82497C-17FC-4A52-B230-404B3D74FA3A
• Deleting-64B237FE-B629-4C28-8ED8-1BFBB0E91801
• Deleting-D514B888-6030-4875-8AC3-1023E8B856AD
• Deleting-532C128D-14E1-464B-8453-3B37645EF36C

Each one looks like a iOS home folder in structure.

The space is reclaimed only when the Machine is rebooted.

Any ideas? thanks