Warning: Undefined array key “filesize” in Images_Optimizer.php

We received a lot of emails last night with these warnings from the cron (wp cron event run --due-now --quiet):

Warning: Undefined array key "filesize" in /wp-content/plugins/sg-cachepress/core/Images_Optimizer/Images_Optimizer.php on line 191
Warning: Trying to access array offset on value of type bool in /wp-content/plugins/sg-cachepress/core/Images_Optimizer/Images_Optimizer.php on line 191

Seems something is going wrong or not handled correctly in your plugin. Please resolve soon, so the stream of cron notifications about this will end. Thank you!