Derek,
Thank you so much for your response! I am manually running the report, going to Reports>Tickets>Ticket Statuses. I've been doing it this way for a few years now, but only recently after the upgrade to v13 did it change behavior on new tickets we process.
I took a couple screen shots for you. For the chart setting, I have open and closed tickets checked. I'm not using any filters, grouping by Group, over a selected week timeframe.
If I run the report for the week in which we were still on version 12.xxx, you see it shows closed tickets just fine. Then if you look at the next screen shot which is for the week after I did the update to v13, it no longer shows closed tickets, even though our departments definitely did closed tickets during that time. So any new tickets we close don't show up in the report, but if I run a report back to tickets that were closed before the upgrade, they show up just fine. So something is different about tickets that we close now in v13 compared to v12.