I have XCTU 6.3.5 for MacOSX, I connected the xbee s2c to a USB explorer and configured in API mode router, this worked fine, but when I tried to connect again to the XCTU I couldn’t.
With the same USB explorer, I can connect other xbee s2c in coordinator mode without problem.
I already tried a troubleshooting guide but doesn’t work.
Try reinstalling the firmware onto the module with the recovery tool in XCTU: https://www.digi.com/resources/documentation/digidocs/90001458-13/default.htm#reference/r_xbee_recovery_tool.htm