If you are using any Caching plugin then you should not cache the forums part. We use Cache Enabler, the very simple caching plugin. You can exclude forums, topics etc. of bbPress using the following regex.
Now, we cache our sites in a simpler and better method. We use a wordpress plugin named Simple Cache. And we shall order Nginx server to serve the cached content bypassing the database query and PHP.
Accelerated Mobile Pages is a Google backed project for faster delivery of your website content to the mobile device users. Search engine shows AMP symbol.
The best plugin for caching sites on Nginx server is to use no plugin at all. Nginx has built in caching module which is called FastCGI. It is the best performer on LEMP stack.