I set a value kerning for a glyph and lock it to be consistent with other glyphs that has the same shape. Suddenly, I notice that there are glyphs should be consistent with original glyph, but it is not. When I check the original glyph, I see that the lock is unlocked, what is the reason for that?
that has to do with glyph and class kerning. It is explained here: Kerning | Glyphs
In short, kerning is always a pair, never a single glyph. If you see the right lock open, it is because it is an exception with the glyph that follows. You can compress kerning in the Kerning window to eliminate exceptions.