Extreme slowness when creating backup
I've been using Acronis for years with no problems, I'm currently on 2019, Build 17750.
I'm backing up an internal PCIe SSD (224GB in size, about 80% full) + an internal HDD (1.8TB in size, about 80% full) to a internal separate HDD backup drive (5.45TB in size, also about 80% full).
There's nothing unusual about this for me, I've been doing it for years and Acronis usually manages to create a full backup of about 450GB in size 2-3 hours including validation.
A few weeks ago I noticed the backup was taking much long to complete - up to 24 hours - here's a screenshot of a backup that had been running for over an hour:
I first uninstalled and reinstalled the software, scrubbing the registry in-between - this made no difference.
I ran VSS doctor (log attached) and it shows an error with Disk I/O load, but I don't know what this means:
I'd be very grateful for any advice.