Worked once but not subsequent times

I scanned one of my servers and got data. I made some changes and scanned again. It sat on 32% for a long time and then 96% for a longer time. Over 24 hours later, it finished but had basically nothing in it. Said, “Number of hosts scanned: 0”. What am I doing wrong?

Ok, it ran but…
Scan duration: 2 days, 3 hours, 23 minutes, 43 seconds
Seriously? Is that normal??