boot – Ubuntu virtualbox failing to start

I have been running Ubuntu 20.04 inside VirtualBox (version 6.0.6) on my W10 host PC. Things were fine the other day, but now I have something along the lines of the following message when I try to start it up:

/dev/sda5: recovering journal
*ERROR* Failed to send host log message

I have allocated 8GB RAM and 4 CPUs to it, and when I set vbox up I gave it 25GB storage. My Graphics controller is set to VMSVGA but I have tried changing it to VBoxVGA as well as VBoxSVGA, neither of which worked. I also tried disabling 3D Acceleration, all to no avail.

It was pretty new with very little installed.. However, I was trying to learn Apache Airflow using Docker, so I have a few things set up for that, but I was only following a tutorial with not a lot of space used. When I last logged on I noticed that I had a space warning, which I was very strange because I can’t have possbly used up the remaining 15GB storage (accounting for 10GB for the OS)! Could Docker have caused this problem?

I’m quite in the dark as I’m very new to ubuntu, virtualbox, and never used docker in the past.