Allowed memory size

Basically, Your server rand out of memory before being able to complete the page render. This isn’t a FPW issue per say, but more of a general, “you’re trying to return too much data in one page load” issue. It just happens that FPW is the last nail in the coffin. It could just as easily be a different plugin or widget that would hit your server’s memory limit.

There are many, many reasons you might run into this out-of-memory issue. Are you trying to return a large number of posts (more that 5 or 10 at a time)? Do you have a large number of plugins enabled? Do you have a lot of widgets running or a specifically lot of FPW setup on the same page view? I’d try configuring your page loads to & widgets to return fewer posts an see if that helps.

The plugin won’t “fall into a loop,” no. Again, this completely depends on the settings you’re using in the widget(s) and elsewhere on the site. if you’re not limiting the number of posts returned, or returning a very large number of posts, or using many FPWs you will indeed run into issues. Again, this would be true of any code/plugin/function that scans a large DB for posts. It’s not a FPW issue exactly, rather your specific use is running into a common issue with large post tables.

On the flip side, I’m using several instances of FPW on a site with about 1.5 million post records and about 3 million post meta records without issue. It really comes down to configuration. FPW is intentionally designed to allow advanced users vast control over what is queried & returned. This will always leave room for queries that are unsafe/not ideal for large datasets.