Hi - the "F" being displayed in the gear indicator display means the transmission has detected a fault, which results in the harsh shifting that you are experiencing & could also cause it to go into limp mode (stuck in one gear). The first thing to have done is to have the gearbox checked for fault codes using a diagnostic tool to see what codes are stored. It could be down to many different things at this stage & the codes will help narrow it down. Common problems are with the valve body which contains the gearbox ECU or internal faults inside the transmission. Both are very costly to repair I'm afraid.
This of course needs to be confirmed with a diagnostic check
Best regards, Paul