So I have a rockford fosgate r400-4d amp driving four speakers in my tacoma. It's been installed for about 3 years with zero issues and is not abused (still running stock speakers). The other day while driving listening to a podcast at normal volume the amp stopped outputting anything to the speakers. The amp never entered protect mode and still appears to be powered on (solid blue led).
Here is a summary of the setup.
Stock head unit
Line output converter (2channel)
RCA input into the r400-4d (using 2 channel input mode)
I use the RCA passthrough off this amp