Had a day that only showed 45 minutes usage a few weeks ago, due to travel/time zone differences between when I slept at the destination and my home time zone. (Seems idiotic that a device that connects to a cell tower doesn't have the ability to adjust to "local" time, but ResMed apparently didn't think that was an important feature.)
While looking at that specific date in OSCAR, I opened the Data menu and chose Purge Current Selected Day, All Except Notes. Then I reran Import CPAP Card Data. It re-imported that one date, and now it displays properly and shows true usage. I had thought I lost the data entirely by packing up the machine too quickly, but fortunately the data was still there. It just wouldn't import without help.
I tried the same thing on a date where I stayed up too late working on a project, and it fixed that day, too.
Now if I can figure out how to directly important oximeter data from my Nonin 3150 BLE for the dates where the Bluetooth connection tanked . . . don't have a Windows PC, and can't figure how to get that working from Ubuntu at the moment.