Backing up my catalogue on exit was very slow. It seemed to stop midway. I cancelled it, but it still didn't finish. I had to canel in the Task Manager. I have Test Integrity before backing up and Optimize catalog after backing up enabled.
Drive/Folder: The backup catalogue is stored on a set of three ST8000DM004 Seagate Barracuda 8TB 7.2K RPM SATA-6GBPS 256MB drives configured as a two-way mirror storage device. My Catalogue is on the same drive.
This may not be the 'soluiton' you wanted to hear but I'll go ahead and suggest: Don't use LR's rather weak backup process. For you it is slow but worse, it only backs up your catalog. You really, really want some backup utility that backs up the catalog, all your images, presets, profiles and everything else on your computer you can't afford to ever lose.
Get a decent backup utility, turn OFF LR's prefs to backup.
Author “Color Management for Photographers" & "Photoshop CC Color Management/pluralsight"