I doubt I ever came across such an occurence. However, "soit... " is used by itself to posit something, to state something for a later argumentation and I guess could be translated to "let there be". It's used in philosophy and mathematics, less so in everyday life. One exemple would be: "Soit x, une variable dont la valeur est 18." A similar use is to mean "that is" or "that means". More commonly, "soit" is used to denote a choice between two things. In such cases, "soit" comes in a pair. For exemple: "Soit je vais recommencer ce travail, soit je vais l'abandonner." Or: "Je vais aller soit au cinéma, soit voir un concert." Maybe the usage you came across is one of those three.

I would rather say that it introduces the said "occurrence". Could you give us the ending of the sentence ?