I have no clue what is causing this and I cannot reliably reproduce it (and unfortunately cannot share my PBI file). However, sometimes Power BI will only load the first 1000 rows of a table to the model, like a Power Query preview, but the model itself actually will only contain the first 1000 rows. Can anyone reproduce? It seems to occur when there's some sort of merge function in the query, but I'm still clueless as to what is causing this. Refreshing the data model will not fix it.