After doing some more testing and research on this issue, I discovered that the issue is being caused by the Planned start and end date in the project being the same date. These projects are being created via a process that fires off when an idea is approved. The process simply calls the system action "convert idea to project" and specifies not to "copy financial properties and financial plans"
Nevertheless, I see that starting the day after the upgrade, projects created via this process do have a "planned cost start" and "planned cost finish" date (which are both the same.
Why is it happening like that?
"planned cost start" and "planned cost finish" date had defaults set to today's date on both Idea and project objects.
Removed defaults for "planned cost start" and "planned cost finish" attributes for both Idea and project objects.