Obviously you are dropping one hot leg somewhere.
After purchasing our 5er, I went thru the load center and tightened all screws on the breakers, neutral bar, ground bar, and all the 12 volt screws. Found many that were only marginally tight. That is the first place I would look. While there look for discolored wires that may have gotten hot. Make sure power is off while in there.
Could be a flaky adapter with bad connection that sometimes makes and sometimes not. You may have to take it apart and check connections. Again look for discoloration.
Could be a flaky main breaker in your load center.
Intermittent problems are the worse kind.