Heyo!!
I've found the fix to chat problems,,
Just follow the steps exactly::::
When you're facing problems in chat,
download SbSettings froms cydia>Go offline in chat> logout from fb app> close the app still active in multitasking>slide your finger along the top bar in order to open sbsettings> select respring> once respringed, open fb , sign in and wait for everything to load up once (this is important, have tried) > go to chat, go online..... And WALA!!!! Chat must work now...!!!
Note:::: evrytime you press the home button and try to go back to the chat, the same thing starts again