404 errors for custom post types

Hi,
We’ve been having an unusual problem with the Optimizer plugin. Sporadically, several of our custom post types start returning 404 errors for all of their pages. If I clear the Optimizer cache, all the pages start loading again. We had a similar issue a while back on a separate client site where their homepage would return a 404 error until I cleared the Optimizer cache, and then it would work again (they finally disabled Optimizer since it was affecting customers).

Is this a known issue, or is there some way I can try to debug what’s happening? I’d hate to have to disable the plugin since it has been speeding up our page loads. We are on Siteground hosting. It looks like we have version 7.3.4 of the plugin at the moment, but it’s been happening sporadically for a couple of months now.

Thanks for any help or advice!
Matt