When sending "large" MIDI SysEx (System Exclusive) messages over USB to 5 pin DIN ports, some throttling by the sending software is required. Otherwise, USB data rates will quickly overflow the MRCC's buffers since the data is coming into the MRCC much faster than it can be sent on 5 pin DIN ports. Over 5K bytes would be considered "large".
To ensure reliable SysEx transfers, make sure the software sending SysEx messages has some delay between buffers. Also make sure buffer sizes are set to what is specified by the gear maker that is receiving the SysEx messages.
For example, using the venerable MIDI OX, open the SysEx configure window:
Click View -> SysEx...
In the SysEx window, click SysEx -> Configure...
Uncheck "Auto-adjust Buffer Delays if necessary".
Set "Delay Between Buffers:" to 100 Milliseconds.
The "Delay After F7:" parameter should not affect the transfer, but it may be required by the receiving MIDI hardware. Follow the instructions provided by the maker of your MIDI gear.