Empty Partitions After Manual Refresh

I've been attempting to load data into a table with incremental refresh on an online model.

Setup executed without issue, but only the latest partition (for the year 2021) had any data. I know for a fact that the 2018 and 2019 partitions should have data, so I attempted to refresh them via SSMS. I ran into this error:

I attempted to manually refresh the 2018 partition and confirmed that there's some sort of issue. As you can see here, the query is using the correct bounds, but unfortunately returns zero rows:

I'm at a loss at this point for how to proceed.