Thanks for bringing this to my attention.
I found it was a minor error in the package that only showed up under versions of PHP 7.2 or greater. I've found this mistake and have corrected in version 1.2 of the package, which you should be available to you now.

If it's not showing up yet, the line in question is found in image_map/blocks/image_map/controller.php
This line simply needs to be deleted:
protected $btCacheBlockOutputLifetime = CACHE_LIFETIME;

You can manually delete that line if it's quick for you to do, otherwise just install the latest version.

Working flawlessly.

Thank you.