[Discuss-gnuradio] GRC freezing and showing stream of "LLLLLL"

Hello,

I was recently working on a flowgraph, which involved using both a USRP Source, USRP Sink block and a QT fosphor sink block, and when running my flowgraph, GRC froze and displayed a stream of "LLLLLLLLL". I noticed that if I replaced my QT fosphor sink with a QT GUI Frequency sink, the problem goes away. I just wanted to know if anyone could tell me what this stream of "LLLL" means and how does someone typically fix their flowgraph to stop this? If it helps, I am using on a Ubuntu 16.04 system and am running GNU Radio 3.7.12.

Thanks,

Jose Ruvalcaba