Why is the global mobile data usage higher than the sum over all the applications? On my Samsung Galaxy Note10+, the mobile data usage shown via the settings is much higher than the sum of the amounts (given below the global one and the graph) over all the applications. Why?

For instance, on 2020-01-01, it shows 10.20 MB, but the individual amounts for the applications are 576 + 386 + 362 + 283 + 65.12 + 53.13 + 44.76 + 34.35 + 24.85 + 21.33 + 16.96 + 13.56 + 10.25 + 9.48 + 9.45 + 8.91 + 5.41 + 3.54 in KB and 878 + 311 + 179 in B, which gives only about 1.9 MB.

EDIT: This seems to be a bug since after sending a big mail (several hundreds of KB) with K-9 Mail, the global data usage increased as expected, but the data usage corresponding to K-9 Mail is still 179 bytes only!
Many Samsung S10/Note10 users are affected by this issue as this can be seen in this thread. So, this is a bug, and there's nothing one can do, except waiting.