This looks similar to this issue
Unfortunately in some cases (sometimes due to upgrades, sometimes due to virus checkers, sometimes ???) the Drafts lose their proper access rights to the local Draft files and cannot be deleted / modified.
We have never been able to repro this in house but the only currently known workaround is to make sure those drafts are not locked and owned by you.
The drafts live in the /Users/<your user name>/Documents/Roblox/Sandbox/<placeid>/<userid>/drafts folder, likely is the folder that you last modified in the Sandbox folder.
Currently the best advice I can offer is to make sure in the drafts folders all the files are owned and writable by your local user.
Deleting these files should also get rid of the drafts.