You are running VirtualBox 6.0.0, the buggiest member of the 6.x branch. Please upgrade to 6.0.4.
Next, you are running the Guest Additions '5.0.18_Ubuntu'. That is not VirtualBox Guest Additions, those are from the Ubuntu fork, and they're ancient. Please purge and replace with VirtualBox 6.0.4 additions.
Ok, everything seems normal until :
16:18:11.547454 GUI: VBoxGlobal::sltHandleCommitDataRequest: Emergency shutdown initiated
16:18:11.547788 GUI: Request for close-action to save VM state.
"Emergency shutdown" sounds quite serious, and it doesn't sound like something VirtualBox decided to do on its own. It sounds like a host management feature. Is it possible that your host is overheating? Is it battery powered? Could it be being preempted by a parent backup process?