+1 on the solder connections. I’m pretty sure this has been covered but…
I purchased 2 new Kingston cards and formatted them with the SD format software utility. After a week or so of no issues and out of nowhere, as I’m starting a print the build plate dropped down into the vat and the machine proceeded to cycle on what appeared to be the same layer. The laser flashed, it peeled, then the laser flashed again, etc. I also noticed the layer counter was not correct.
I removed my card reader and the entire inner row of pins along with one of the end pins on the outer row were resting loosely on their pads. After de-soldering and removing the outer pins and re-soldering the inner row then the outer, everything is working very well. I think what’s happening in some cases is there’s enough of an electrical connection being made to let the card reader communicate. After enough time and temperature changes the loosely connected pins are losing contact making the machine behave erratically. If you’re comfortable with a soldering iron and de-soldering wick it isn’t too difficult. Just be careful not to over stress the pads on the circuit board.
I’ve had my printer for 9 months and wish I had checked the pins sooner. It’s worth a look if you start to experience problems.