Party "testing various features to make poker more fun and entertaining." Certain tables apparently hidden from winning players that contain a certain threshold of "new" or "inexperienced" players.
Louchiere, SXC Attribution with Notification

A representative from PartyPoker has, in rather uncertain terms, confirmed that they are at least “testing” a feature that apparently grades tables, and removes them from the lobby of regular players.

A Party representative posted publicly Thursday that the company is “testing various features to make poker more fun and entertaining,” including looking for ways to facilitate “players of a similar ability” playing together “in the early stages” of their online poker experience.

Reports began to surface earlier in the week on multiple online poker forums, including German and Russian community forums on PokerStrategy and on English-language 2+2, that players were seeing fewer tables after logging into the client.

A variety of screenshots and YouTube videos apparently show fewer tables after a player logs in, or shows that lobbies of a “new” or “losing” account has more choices than that of a “winning” account.

Although reports vary, a consensus seemed to be that players with “winning” accounts saw fewer tables, and in particular, less “fishier” tables, at low stakes NL. New accounts, or those with lifetime negative balances, saw more.

After days of speculation, an official representative from Party Poker posted the following on 2+2:

We are continually looking for ways to balance our poker room ecology. As we have said before, we are testing various features to make poker a more fun and entertaining game for both new and inexperienced players. Our extensive research shows that new and inexperienced players enjoy the game more and continue playing for longer if in the early stages they play with players of a similar ability, this includes, but is not limited to our welcome lounges. These players are free to play on any table they chose.

Although far from clear, apparently this new feature in testing is speculatively hiding specific tables—rated with a certain threshold of the number of new or losing players—from winning players.