First aid in these cases:
1. switch to default bootstrap theme to exclude custom theme issues
2. test only English version to exclude language pack issues
3. switch off all none core plugins (not ported for version 2) to exclude legacy issues. F.e content plugin.
If site works, then problem is somewhere else not in core and not in upgrade.
Check each issue if it's still appearing. But always in bootstrap/English/core plugins combination, because otherwise everybody will look at wrong place. And use debug mode.
No forum (I pus the forum link and nothing on the page - blank page)
- htaccess or sef url (url configuration) problem or left already not used files (run files integrity test)
- no caption on the comment menu
- rendering or translating issue
no news month (I put it on the menuarea, but menu don't appears)
- try to install menus at theme area at first. Try refresh menus button. Put it at first on the list. (It sometimes happens when menu before has problems - again problem is somewhere else)
no images on the admin page (example in download)
- htaccess issue, htaccess from version 2 is different than in version 1, maybe you have old one there...
I wish you luck and I really enjoy for your themes for version 2