Yes it is probably an old “lock file” that is still present.
In Finder, Go > Go to Folder and type or paste:
~/Library/Application Support/audacity/
Click “Go”.
In the “audacity” folder that opens, open the “audacity.cfg” file in TextEdit and look for the line underneath [Directories] that starts with TempDir=. Carefully select and copy everything after the equals sign. Mine is var/folders/c0/8p18hd453p3_433cf9_595b40000gn/T/audacity-gale.
From Audacity 2.1.3, Audacity’s default temporary directory is at /Users//Library/Application Support/audacity/SessionData.
Then in Finder, Go > Go to Folder, paste in the path you copied and click “Go”.
In the folder that opens, delete the file “audacity-lock-”.
Gale