The failure mode I've seen most often is that one bit of each byte will fail to store or retrieve correctly. Memtest86 will store an FF and read back an EF, for example. Computers with this problem may boot, but crash often.
The other failure mode I've seen is that a RAM module will fail to be recognized or cause a POST error, and the computer will not boot until it is replaced.
Neither happens often, but I've seen each of these more than I'd like. I could imagine both issues might possibly be less likely with a solid soldered connection vs. a port which can become damaged or dusty, but I don't have enough experience with soldered RAM modules to be able to say anything about its reliability.
The other failure mode I've seen is that a RAM module will fail to be recognized or cause a POST error, and the computer will not boot until it is replaced.
Neither happens often, but I've seen each of these more than I'd like. I could imagine both issues might possibly be less likely with a solid soldered connection vs. a port which can become damaged or dusty, but I don't have enough experience with soldered RAM modules to be able to say anything about its reliability.