The only work around I’ve come up with when I encounter this problem is…
Open ‘Preferences’
WIN/LIN: In the top menu, select Edit > Preferences. (Press Ctrl + U)
MAC: In the top menu, select Harmony Premium > Preferences. ( Press ⌘ + U)
Select the ‘Render’ tab
Then under Multi Threading, change ‘Number of Rendering Threads (0=auto)’ change from ‘0’ to a ‘1’ and then hit ‘OK’.
Then try out an export, hopefully this helps out!