Reaper freezes horribly here occasionally, after losing connection to USB MIDI device. See images in links below.
https://1drv.ms/i/s!AtA-M3AOJ19whAucdUzziMQxNiiS
https://1drv.ms/i/s!AtA-M3AOJ19whAoFGzJ-Z9xX3ckt
https://1drv.ms/i/s!AtA-M3AOJ19whAnRiuS5Ty4AxpWb
Suddenly, one popup appears "Reaper - wait for MIDI output device". Then another, and another..... after some minutes there are houndreds of popups, and Reaper is completely locked. Disconnecting MIDI device does nothing, powering down device also does nothing, Reaper is caught in eternal loop. No way to stop this, no way to close Reaper. The only solution is to restart PC.
Please, implement some timeout. Or if it cannot connect, give option to manually skip device. Or at least make it possible to exit Reaper and start it back again. As it is now is not the optimal way to deal with lost connection from device.