I'm not sure whats happened now but I cannot get back to anything that works correctly.
i) I deleted the modified plugin.pyo file and renamed the old one back to the same name and rebooted.
ii) restored from a backup
iii) from the plugin menu removed imdb and then downloaded again
In every case I now get on the details page:
"IMDb Download failed: invalid liereral for flaot(): 25 November 2017"
The date changes depending on film selected to check