Hello. Some of what you are experiencing are not actual bugs
- not sure about the report of some events not showing up as an option to sync with in DT Register. If the event in JEvents is repeating, unpublished, or already past, it will not show up as an option in DT Register. That's how it's always worked for the sync option.
- the checkboxes in JEvents you say are not staying checked has absolutely no connection to DT Register and never has. That would be a JEvents bug. You can try upgrading JEvents... or better yet... get rid of it and just use the new DT Register calendar.
- if you admin email is blank, it's because you haven't set it up yet!
In 2.7, you configure this instead of it just being hard-coded. Go to configuration -> Emails. You'll find the admin notification email and subject needs setup.
- not sure about the names report for the attendee's list. I don't think this is the case, but I'll check it out. No other reports like that. Thanks.