I am also having issues. I have 3.1.5 of phpbb installed. I just get the following.
Repair any missing information: Continue
WordPress database error: [Unknown column ‘forums.forum_topics’ in ‘field list’]
SELECT convert(forums.forum_id USING “utf8mb4”) AS forum_id,convert(forums.parent_id USING “utf8mb4”) AS parent_id,convert(forums.forum_topics USING “utf8mb4”) AS forum_topics,convert(forums.forum_posts USING “utf8mb4”) AS forum_posts,convert(forums.forum_topics_real USING “utf8mb4”) AS forum_topics_real,convert(forums.forum_name USING “utf8mb4”) AS forum_name,convert(forums.forum_desc USING “utf8mb4”) AS forum_desc,convert(forums.left_id USING “utf8mb4”) AS left_id,convert(forums.forum_type USING “utf8mb4”) AS forum_type,convert(forums.forum_status USING “utf8mb4”) AS forum_status FROM phpbb_forums AS forums LIMIT 0, 100
No forums to convert
No data to clean
Starting Conversion
