Distiller failing to generate images from FM 2015 since May 7th 2018

When publishing documents using FM 2015 (and FM 2017) to all html formats on a Windows 10 computer, distiller no longer is activated so no images are being generated in the output from the files.

The generate images using distiller check box is activated in the publishing settings.

I have not experienced this issue before and is new since May 7th 2018 (the last time I successfully published files with images included), so suggests a recent upgrade to something is responsible.

Any suggestions as to how this can be fixed?