"FMallocUnused" is immediately bellow 0. "Untracked" is reported to go below 0 after very long playtimes (over 36 hours).
Reported in version 4.25.3(CL 13942748). Tested and found negative values for "FMallocUnused" in versions 4.25.3 and 4.24.3(CL 11590370).
Result: Some memory values are negative.
Expected: All values are above 0.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-100575 in the post.