I heard this the other day, and I can't find it in my dictionary. From the context, it seemed to be used with the meaning of "disappointing," or "a let-down."
I'm more familiar with the adverb しょんぼり, meaning "down in the dumps, downhearted, blue". Looking into this some, I've discovered related terms しょぼくれる, しょぼしょぼ, しょぼん（と）, and しょぼたれる, all with the same basic meaning.
From this, I would guess that しょっぽい is part of this same group. The っぽい ending is an adjectivizing suffix meaning "-ish", so presumably しょっぽい would mean "bluish (of mood), kinda depressed or depressing".
As others have noted in the comments to the question, the asker's しょっぽい may be a mis-hearing or alteration of しょぼい, itself derived as the simple adjectivization of the root しょぼ + い.