Currently I'm having an issue in Reaper where my midi keyboard (connected via USB) will send midi note signals when I open the program. But once I hit play in the DAW, it won't send any more messages until I go into preferences and reset the midi devices. I have no other issues at all when using other DAWs like Ableton and Logic.
What keyboard is that exactly? USB devices losing connection is very often related to USB power issues (which may also show up with host software A but not B).
Please try a different USB port (not all USB ports can deliver sufficient currents for high power devices), use a powered hub, or (if possible) a power supply for the keyboard as opposed by using "bus power".
MIDI glitch/issue
Linear Mode
