The simple definition of hot short is “a metal which is brittle when
at or near red heat”. With silver alloys this usually caused by the
presence of a low melting point phase at the grain boundaries of the
silver grains. In the example I gave of phosphorus de-oxidised
sterling silver, excess phosphorus in the silver forms a
copper-phosphorus low melting point phase at the grain boundaries.
Other impurities which give the same effect are tin and lead; both
constituents in low melting point solders which could be included in
your silver alloy if present in your melt feedstock.