No, that's clearly local production, not
mint of
Rome.
Apparently the engraver just left out the second Σ of ΣEBAΣTOΣ. Such things happened. No such error is recorded in
AMNG,
RPC, or
Varbanov.
Certainly legends were generally
engraved after the
types, and quite possibly by a different engraver. Your coin doesn't prove different engravers, however: there is no reason that a competent engraver couldn't leave out a letter in the
legend, making a mistake just as even the best of us do quite regularly!
I don't see thε shift in the Δ. I see an ordinary Δ, a little
bit compressed and with one of the upward strokes extended beyond its meeting point with the other one.