The only way to migrate wpForo without any issue is migrating all wpForo database tables and your WordPress user tables. So in the target WordPress the users tables should be overwritten with old one and make sure the prefixes are the same:

User tables:

• wp_users
• wp_usermeta

Forum Tables:

 All tables with wp_wpforo_ secondary table prefixes.

Then you should care about the files. You should move /wp-content/uploads/wpforo/ folder to the same directory of the target WordPress.

Once all is migrated, go to Dashboard  >Forums > Dashboard and click the [Delete all caches] button. Then go to Dashboard > Forums  >Settings > General Tab make sure the base URL is correct and click the [Update Options] button.

1-) You will need to move all files in  /wp-content/uploads/wpforo/

2-) You will need to move to the new server then import the following tables:

wp_users 
wp_usermeta
wp_wpforo_accesses
wp_wpforo_activity
wp_wpforo_attachments
wp_wpforo_forums
wp_wpforo_languages
wp_wpforo_likes
wp_wpforo_phrases
wp_wpforo_pmfolders
wp_wpforo_pms
wp_wpforo_polls
wp_wpforo_posts
wp_wpforo_post_revisions
wp_wpforo_profiles
wp_wpforo_subscribes
wp_wpforo_tags
wp_wpforo_topics
wp_wpforo_usergroups
wp_wpforo_views
wp_wpforo_visits

However, I do have most of the paid add-ons so maybe you will not have some of those tables such as wp_wpforo_polls for example. Also, if you have done any CSS customization to the forum remember you will need to copy and paste those to the new forum as well.