The artist doesn't say explicitly, but the timing makes this a near-certain reference to Mumei's 1,000,000-subscriber stream the other night (an unarchived karaoke), which was plagued with so many technical problems that the poor girl nearly lost her voice from stress-screaming.

The real pressure she felt was from having to perform that night. Otherwise it was very likely she'd tip over to 1,000,000 without streaming at all. Moomans were likely unsubscribing en masse just to try and buy her time.