Sorry to hear about the recent issues you have been experiencing.
Some things to check.
1. Open the MIDI Monitor in Studio One, do you see MIDI activity from every key?
2. Check to see if the M-Audio Keyboard was accidentally switched to its advanced mode. Check the Oxygen documentation for this mode, so you can switch it back if it was engaged.
If the issue remains, please create a ticket to technical support. Here is a link to create a ticket: http://support.presonus.com/hc/en-us/requests/new