Same happening to me. Started in early-mid June of this year and has continued to get worse since then. Both google & bing crawlers report server 500 errors, and my web hosting support team has this to say:
“This means that the /public_html/…/wp-content/plugins/jch-optimize/jchoptimize/libs/HTML_Optimize.php file contains a reference to the ‘JchOptimize\JSON_Optimize’ class, but this isn’t defined elsewhere in the php code that your site runs.
Either the ‘JchOptimize\JSON_Optimize’ class would need to be defined, or what’s calling this class (which looks to be the jch-optimize plugin) would need to be disabled.
Looks to me like i’ll have to disable it and find another plugin that does css/javascript minifying & combining.