Units - is feature from the model summarized in matrix visual
Units Measure - is a simple measure Units Measure = SUM('DATA'[Units]), returning absolutely same result, but...
As you can see on screenshot, there are blank rows in Units Measure column. More drammatic behavier is when i remove Units feature from Matrix - i can't see those blank rows within Units Measure column. For instance i will not see rows with Customer like "AGROPRODUCT", meanwhile the Total will be shown correct . Moreover, if gonna create another measure like Running Total, based on this measure - you will not get 17441 - the final result will be much less, due to missing data.
I suggest there is a bug either in measure rendering or in measure logic itself.
Actually, it was noticed during ABC Dynamic Analysis on my modeal and data, and measures and model were much more complicated. Then i saved just single small table with 3 features(CUSTOMER, DATE, UNITS) and wrote simple measure - bug has been replicated.
I'm using PowerBI Pro Version: 2.76.5678.782 64-bit (December 2019)