Hello Mark,
The thumbnails work perfectly when the Really Simple SSL plugin is deactivated. Have not tried switching to other theme in fear of damaging the website beyond repair. This is a purchased theme (Peak by OnionEye) and used broadly used.
I hope you have some other tips to overcome this bug. I read some other posts with similar problems which seemed to be resolved however the solution was not posted.
Appreciate your support !!
Thanks,
Willem
