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I’m not a fitness guru but you’re way short on information. Read what you wrote and tell me objectively what you would do with that info if you were responding? Your question boils down to: I used to work out, then I stopped, then I started again, worked shoulders and chest, arms on fire, then arms not on fire, what’s up with that?
More detail on your routine, diet, and current physical condition are necessary to answer what I think you are may be trying to ask - Is my lack of soreness a sign of an inefficient workout?