There are several things that could affect the alignment of the text. The font asset, its metrics like Ascender, Baseline and Descender and the margins. Unfortunately, the images above don’t provide enough information to know what exactly is contributing to the result you are showing above.
Included in the example scripts provided with TextMesh Pro is a script named “TMP_TextInfoDebugTool.cs”, add this script to this Bob text object. Then enable Show Characters as per the image below.
This tool will allow you to visualize the bounds of characters (yellow box), Ascender, Cap Height, Baseline and Descender (blue lines) of each characters. So when using bottom alignment, the bottom blue line (Descender) should be aligned with the bottom of the RectTransform / margin in case it was changed. Margins can be seen in the Extra Settings.
Here is an image using the word BOB but with Futura Bold (I don’t have Futura but the metrics should be similar).
Left with object selected where the Descender is hidden behind the yellow margin line. Right un-selected where you can see the alignment is correct.
Now we just need to figure out why in your case you are not getting the correct results.
P.S. The version of TMP for Unity 5.6 should 1.0.56 so 1.0.54 seems wrong. See the following thread which includes direct links to download TMP.