you should attempt to add the CSS (if its from your theme) to the main CSS file.
Indeed a solution.
The problem is depending on your hosting environment autoptimize will cause problems with inode generation.
Just to be clear, hosting restrictions on inodes do not indicate a problem with Autoptimize or the number of inodes it might generate, but rather a hosting limitation.
[Autoptimize] will generate a new file per page for minimal speed improvement
Autoptimize will generate a new file per page for page-specific or request-specific scripts (which is optimal). Page-specific or request-specific CSS is relatively rare and a non-issue. Both, however, become non-issues if/when the entire HTML response is cached; and, above-the-fold CSS is inlined or all CSS is inlined (in the instances in which inlining all CSS is the most performant solution).
If you have a small website with a few posts by all means use auto optimize but I strongly recommend following better practices.
Inode generation is not poor practices. It’s restriction is, however, part and parcel to cheap hosting plans so the host can continue to oversell the server.
More to the point, however, one can easily include or exclude whatever inline CSS or .JS one wants to include or exclude for concatenation with Autoptimize. There are additional mechanisms in place to keep cache size under control as well (if one is on an oversold hosting plan, which all shared hosting is).
Lastly, one can find a multitude of search results about people getting into ‘too many inodes’ issues with W3TC; and, assuming my Google Fu is fully functional, precisely none about Autoptimize.
Best,
AJ