Thanks. I can reproduce.
Here is a workaround:
1. Quit Photoshop
2. Back-up these two files which are located in the Photoshop application folder at the following location:
- Presets/Scripts/ArtBoards To PDF.jsx
- Presets/Scripts/ArtboardExport.inc
3. Download the zip file from here and double-click it to unzip:
https://adobe.ly/2kc2snD4. Place the two files in the same folder as above
Presets/Scripts/ (You may be asked to provide your administrator password to replace the files)
5. Restart Photoshop