If you should experience that recorded notes are being “cut off” (staccato) when recorded in the sequencer, it could be that you have accidentally added your MIDI Control Keyboard twice on the Control Surfaces tab in Reason’s Preferences:

If this should be the case, just delete any duplicates and see if that helps.

Also, make sure your MIDI keyboard doesn’t send out MIDI on multiple MIDI channels (“Layers mode”, for example).