I checked the latest imported post, it's thread id and what the next thread would be and deleted it from the source (old threads with lot of replies). I got to almost 100% now but got these messages:
In AbstractStatement.php line 228:
MySQL query error [1406]: Data too long for column 'delete_reason' at row 1
xf:import [--processes PROCESSES] [--finalize]
Exception query:
INSERT INTO xf_deletion_log
(content_type
, content_id
, delete_date
, delete_user_id
, delete_username
, delete_reason
) VALUES (?, ?, ?, ?, ?, ?) ON DUPLICATE KEY UPDATE delete_date = LEAST(delete_date, VALUES(delete_date))