"L" error for using file_sink blocks.

Hi,

I am using USRP X440 to build a wireless communication prototype. The host PC is equipped with i9-14900K and I am trying to use two transmit channels and two receive channels of the USRP simultaneously. I feed two generated signal to two channels by the USRP_sink block, and then I download the received data  from the USRP_source  by file_sink blocks. The sample rate I use is 150 MHz for each channel. 

However, I noticed that there are many "L" occurs when I run it. Even if I reduce the sample rate to 30 MHz, I can still see the problem. But if I use qt_gui_frequency_sink to visualize the received signal, it can hold up to 150 MHz without any errors.

I would like to ask the reason for this. What cause the "L" errors? Is it about my ssd's writing speed is not high enough?

Thank you very much.