Square shares hit an all-time intraday high on Monday, rising over 9.5 percent, as shares changed hands at more than 200 percent the average 30-day volume.
But many on Wall Street told CNBC they were stumped as to the exact catalyst of the share move. Financial shuffling like merger rumors, options or short-selling are sometimes the source of unexpected stock moves, but in this case, there wasn't any obvious chatter around Square's mysterious move.
Square declined to comment.
"[I didn't] hear anything new today. Some ebullience in crypto markets could be contributing," said Credit Suisse's Paul Condra.
Square shares are up nearly 200 percent over the past year, and almost 96 percent over the past 6 months, amid some better-than-expected quarterly earnings reports. CEO Jack Dorsey has also embraced the recent enthusiasm in the cryptocurrency market, expanding a feature to buy and sell bitcoin through the app, Square Cash.
Bitcoin was only about 1 percent higher, around $11,554, on Monday, according to Coinbase. But the ongoing "frenzy" around the cryptocurrency may be splashing back around Square shares, said Instinet's Dan Dolev, a Square bull. He said that while there was no big step forward on Monday, the excitement around bitcoin could create new opportunities for Square down the road.
"There's really nothing new on Square today. I think it's kind of ramifications of commentary that was made last week on them testing bitcoin with merchants," Dolev said. "They are now accepting bitcoin everywhere on the cash apps. It's not necessarily that bitcoin goes up, it's more just associated with Square being a first mover.... The question is, will they allow merchants to accept it? I think it's just pure speculation. But if that's the next step, then it kind of goes viral."
Disclosures: Square has been an investment banking client of Credit Suisse in the past year, and Credit Suisse expects to seek investment banking compensation from Square in the next 3 months. Credit Suisse also makes a market in shares of Square. The Nomura Group beneficially owns 1 percent or more of a class of Square shares.