After upgrade, what issues do you have. Layouts now use themes, so your layouts may need to be revised to display properly.
There might be some Deprecated futures that have been removed and/or changed since v 9 but is hard to determine without answering what Planteg requested as what specifically are the problems you are having,
I could not find the v9, 10, or 11 deprecated items but below is a link for v12. However, I bet someone has the list and hopefully see’s this and posts the changes for v9 and so forth.