This Bug was split in too, the other half is tracked as Case 1383114

The Top Memory usage categories add up to more than the Total on some platforms, as Unity may consider more memory as "in use/reserved" than the platform API's return for the System Used Memory Profiler Counter. This leads to confusing displays in the Memory Profiler Package where the total may have a bigger or significantly different variation between 2 snapshots than what the categories in the bar suggest would be different between the two.
This also means that the categories do not add up to the Total.

How to reproduce:
1. Open any Project
2. Install the Memory Profiler Package via Add By Name/ Add By Git URL: "com.unity.memoryprofiler"
3. Open the Memory Profiler and click Import, choose the two attached snasphots
4. Switch from Single to Compare mode and open both snapshots
5. Observe the Memory Usage Overview > Memory Usage bar

Expected: The Reserved of all Categories added up together is equal to the total for each corresponding snapshot
Actual: The Reserved of all Categories added up together is more than the total for each corresponding snapshot

Expected: There should be a clear reason visible in the UI for any differences in the Total
Actual: There is a difference of 0.03 GB between the two snapshots, (27MB to be precise) that can not be found in the differences of each of the breakdowns