In the Pro version there is a cron job that runs immediately after the promotions check is done that will (should) catch the join requests, but for the Lite version there is a Maintenance tool (
Threadmins in the ACP and
Maintenance) called
Group Moderators - Check Users in Usergroups. Running that should pick up any missing moderator permissions.
In the next update I'll have a look at seeing if we can pick up the join requests normally. Not sure on an eta for it atm as I'm completing another project before I can give my attention to Threadmins again.
Thanks for picking up this issue, we really appreciate the feedback from the users.
Matt