[Solved] Problem with WPFORO and WPROCKET
wpForo doesn't purge all caches of wpRocket but only Forum page cache where is wpForo's [wpforo] shortcode, and that pages cache has to be purged by wpForo. There is nothing to do there for us, Forum pages(only that pages) cache must be purged by wpForo that wpForo could work normally.
To solve my problem, WProcket support worked on my site for more than 10 days. They came up with a solution that is acceptable and for anyone who has the same problem as me here is what to do so that WPforo does not accidentally delete the WProcket cache:
1) Install the Rocket No Cache Auto Purge helper plugin, which causes all WP Rocket auto cache clears to be disabled. In effect, this prevents the cache from being flushed when people log into the forum and do other actions that cause the cache to be flushed.
2) Set up a server cron to periodically clean and refresh the cache files, perhaps once or twice a day.
Here's hoping to help anyone who has the same problem as me.
Thanks again to everyone for reading