Firstly AMIRA LogC is identical to ALEXA LogC, so you are using the correct IDT.
If you are on Resolve 14, you could try the “Neon Suppression” LMT, which is an implementation of the matrix that @sdyer posted on another thread here for removing this kind of artefact. If you are on an older Resolve version you can try the DCTL version of the same matrix posted in that thread.
As for the reason that artefact occurs, I suspect it may be a deBayer problem occurring due to the dramatic transition at that edge. If the colours being interpolated are very different, particularly if one or more channels are clipped as here, it is possible for the interpolation to produce “unreal” negative values, which can lead to this kind of artefact. This is only my speculation though.
Using the wrong (sRGB) IDT will not produce the negative values, as the10-bit code values below 95, which represent negatives in LogC, still represent positive values in sRGB.
Finally, when you say “data below the black point”, do you mean “below 64”? The ACES Rec.709 ODT black point is at zero, not 64, so there is nothing below black on output. It is clipped at zero. But saturated cyans in the image may cause the red output to clip to zero. Grading operations which reduce the cyan will lift some additional red out of clipping on the scopes. But that does not mean there was previously anything below zero on output. Does that make sense?