Trying to open 5.21.4 project in 6.4.1 - incompatible version

I'm in the process of migrating 5.14.1 to 6.4.1 via 5.21.4.

I successfully did this for one app.

For the second app, I migrated to 5.21.4 and checked it in. Now, when I try to open it in 6.4.1, I get the following error: 'The project located at c:... \BarterDeals.mpr' could not be opened, because it was created with version 5.21.4 of the Modeler, which is incompatible with this version of the Modeler.

Not sure why it isn't asking me to convert-in-place like the other one or how to work around this.