This is caused by differences in the "left side bearing" (empty space to the left of the glyph in the glyph slug) that are used to regulate the spacing of running text. Turning on Optical Margin alignment might or might not help (possibly make it worse), but the only certain way I know to line up the character left edge vertically in the same frame is to add something like a hair space in front of one and adjust the kerning between it and the first real glyph.
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