Please try restoring the app to factory defaults. Here is how:
1. Quit Strip HTML if it is running.
2. Go in the Applications folder and delete any previous installed versions of the app (if any):
~/Application/HTML Sripper Lite
~/Application/Strip HTML Lite
3. Show the Library folder.
In OS X El Capitan 10.11 or earlier: Pull down the “Go” menu and hold down the alt/option key. Choose “Library” from the drop down list.
In macOS Sierra 10.12 or later: Pull down the “Go” menu and hold down the Shift key. Choose “Library” from the drop down list.
4. Open the Library > Containers folder and delete these folders if they are present:
5. Open the Library > Preferences folder and delete these files if they are present:
6. Open the Library > Application Support > Apimac folder and delete this folder if it is present:
7. Download a fresh copy from our Download Page.
8. Launch Strip HTML in order to recreate from scratch the resources it needs.