Have you updated your macOS recently? I have read about situations where the update to Mojave has affected printer driver.
Try reinstalling the printer driver.
Are you using a fairly long USB cable? This sort of sounds like a flakey connection if it has a connection to the printer ... then loses it.
You might also try printing wirelessly. If you haven't done so, with printer connected via USB, run the "Canon IJ Network Tool". This utility lets you configure the printer so it can join your wifi network. Once completed, you can disconnect the USB cable.
07/31/2023: New firmware updates are available.
05/31/2023: New firmware updates are available.
05/18/2023: New firmware updates are available.
04/20/2023: New firmware version 1.4.1 is available for EOS R3
03/30/2023: New firmware updates are available.
2/07/2023: New product announcements!EOS R8 EOS R50RF-S55-210mm F5-7.1 IS STMRF24-50mm F4.5-6.3 IS STMRF15-30mm F4.5-6.3 IS STM