There has never been any evidence presented to substantiate this accusation.
In lieu of evidence, the propagators of this accusation have relied upon the defining tactic of tawdry conspiracists everywhere: relentless repetition of rumor and innuendo based on alleged inconsistencies until it spreads far enough through the media ecosystem to take on the appearance of being credible. In this case, there was one particular fiction — about where Snowden spent his first 11 days after arriving in Hong Kong — which took on particular significance for this group.
They insist that Snowden, contrary to what he has always maintained, did not check into the Mira Hotel on May 21, 2013, the day after he arrived in Hong Kong. Instead, they assert, he checked-in only on June 1, which means Snowden has 11 "unaccounted-for" days from the time he arrived in Hong Kong until he met with journalists at the Mira in the beginning of June.