Hello,
Not a clue what's wrong with chat, diff in default ui shows only some offsets and sizes are changed. I found quick hack (not really a fix, but works) to make chat working. This is actually permanent settings change suggested by @Mysstie
In DrumsUI folder open file eq2ui_mainhud_mainchat.xml in text editor, in first Page element (Name="MainChat") locate OnShow="... attribute, and after quote insert the following text:
chat_input_fontsize = 15

Save file and reload ui / camp to other character / start everquest if not started
This wil reset input box font size to default each time UI is loaded, and also fix position/visibility of the input box.
Well, at least it works for me
P.S. Modified file is attached.