The alias thing was something on my part, at least in part; has to do with the bot users not necessarily having the right data. I got it mostly working eventually, but it chokes on some posts.
anonymised:
convert.php:364
conversionmaps/phpBB3.map:144
convert.php:753
) 42601: ERROR: syntax error at or near "1" LINE 1: 1 ^
Query: 1
_POST: array ( 'from' => 'phpBB3', 'cfg' => '$PHPBB3_FORUM_DIR', 'verbose' => '1', 'submit' => 'Start conversion', )
Database version: 9.0.3
[Referring Page] http://site.tld/forumlocation/convert.php
the log is more informative, basically a value ends up being null, so there's a SQL syntax error
STATEMENT: INSERT INTO _thread (
id, forum_id, root_msg_id, views, replies, thread_opt, orderexpiry
) VALUES(
784,
,
1135,
6,
0,
0,
0)