Essentially, the game’s spam filter is currently set to catch repeated words and speed of messages submitted and auto-flag certain accounts as spamming, which places them under a temporary mute. However, when lyricists are belting things out in chat, often with repeated words for emphasis? It’s catching their lyrics as well. While the studio is offering help for players unintentionally gagged, there’s still a lag time in removing the restriction, and musically inclined players are quite worried about what this might mean if they get auto-gagged in the middle of concerts. A bit like watching a bee fly into someone’s mouth mid-song.
Source: Official Forums, Patch Notes; thanks to Triski for the tip!