Water Heater-Sometimes hot sometimes not

[51coke]

2014 International Signature 23d with Atwood water heater. On electric mode sometimes we have hot water at the sink and shower and enough hot water for 2 showers. Sometimes we have warm water. Sometimes we have no hot water. Sometimes one person can shower then its cold.
We have checked for loose wires and they all seem ok.
There is plenty of hot water when we use the gas.
Any suggestions what else to check for.
Thank you.