I am having the same issue with RTE not showing after upgrade from 2.4 to 2.5. I am seeing it on two different websites I upgraded this afternoon. One of them used Expresso as the WYSIWYG, while the other used Wyvern.
The upgrade seemed to work, but when I went to test editing an existing entry no WYSIWYG editor appears at all for either site. The content is still in the field, but the field shows the HTML markup. I tried converting the field to the new RTE to see if it made a difference, but the RTE does not show up either (I am attaching a screenshot).
On both of the content entry pages the file upload fields appear at the bottom of the screen below the standard page footer (screenshot attached), as well - and the upload functionality does not work.
These are two separate websites with different 3rd party add-ons, but both are having the same issues so I feel that this is almost certainly a 2.5 issue.
I do have .htaccess removing index.php and I have already tried adding index.php in the general configuration but it hasn’t done anything. Any help with this ASAP would be greatly appreciated. Happy to provide admin access if it helps.