There are a lot of topics about it. All in all exclude wpForo page from caching. Doesn't work fine.

Some caching plugins work more-or-less, some don't, none of caching works 100% well.

Search the forums for rocket cache problems. Some people claim it works for them, still i highly doubt it.

We recommend disable WP Rocket and other cache plugins for forum page. Just exclude the main forum page from your cache plugin. wpForo has built-in cache system designed only for forum part. All cache plugins makes forum data static and you see wrong information, wpForo built-in cache is dynamic and adapted for forum pages.

There should be an option to exclude pages or URLs from WP Rocket caching, just use that and exclude your forum page.