The error you saw may occur when the MySQL data is left in an inconsistent state – and that may be due to another plugin running a query and never fully completing / clearing it.

As a first step, please try disabling any caching or security plugins, then deactivate and activate wpForo again, then activate your cache/optimizer plugins.

If the issue is not fixed, this could be when the memory size is exhausted. Check if your site database memory size is exhausted or not. 

 WordPress database error Commands out of sync; you can't run this command now for query SELECT post_id, meta_key, meta_value FROM wp_3cy42zznwz_postmeta WHERE post_id IN (2153) ORDER BY meta_id ASC made by shutdown_action_hook, do_action('shutdown'), WP_Hook->do_action, WP_Hook->apply_filters, LiteSpeed\Core->send_headers, LiteSpeed\Control->finalize, LiteSpeed\Metabox->setting, get_post_meta, get_metadata, get_metadata_raw, update_meta_cache

Post ID 2153 is my forum page, so the issue is with the page the forum is on. I have a few of these errors too. And it only started after I updated to the new version.