I have imported phpBB->mybb->xenforo recently. Everything is working fine. But the only thing I noticed that the date shown in Attachment browser from Admin panel is incorrect. It shows Jan 1, 1970. Is there any fix for this? The host thread date is correct however.
The attachment date is separate from the thread date, so it's likely been recorded with a value of 0 (which means Jan 1st, 1970). As such, this is very likely an import issue (I would say phpBB -> MyBB as we haven't heard of this before), so unfortunately it can't really be fixed within XF.