In the completion settings on my modules I am seeing the date in the form equal to the date in the database minus one day.
This is a bug.
Just upgraded Moodle to the most recent software.
Open a tracker report in tracker.moodle.org with full details of how to reproduce the problem you are seeing.
You've not really given us enough (any) information to go on here. Which database field? Which version of Moodle? Which completion setting? And so on...
I have actually seen this before:
https://moodle.org/mod/forum/discuss.php?d=331954#p1336848
if I remember correctly I changed themes and the problem went away last time....but all of the three themes included with the most recent version include the bug...I might suggest every single Moodle installation actually has the dates wrong in the database at this point!!!!
The completion date you set on course items is housed in course_modules field completionexpected.
I honestly don't know anything about how completion works under the hood, but I'd be really surprised if it had anything to do with the theme.
That field is set from (as far as I can tell) every activity type by calling 'update_completion_date_event' in completion/classes/api.php
Seems to be working correctly now. So very odd.
Whoever fixed it can you check to see if the LTI is sending the ip address to with the external query?