This is likely normal and due to idle power power consumption.
Note that any power station, including the EB70S, consumes a certain fixed amount of power just to be on. This is independent of the wattage of loads plugged into it. This is usually a little over 1% of the max inverter wattage.
So, if we assume the EB70S has a idle power of say 9w, it would consume 23x9w = 207wh over 23hr even if nothing is plugged into it. That combined with your load consumption of 414wh would be 622wh. Giving it 86% efficiency, which is decent.
A lot of this idle power is consumed by the inverter, which usually has idle consumption around 1% of max power. That is why many power station has eco mode which turns off the AC output when there isn’t enough load for a few hours. Regulated DC also consumes some power, but less. So use DC only if the load is small, or use a lower wattage power station for smaller loads.
Try it with a larger load. My EB70s did 600-620wh over 4 hours (depending on which watt meter I used) with a constant load of 157 watts. Running a residential size fridge in a cool garage it only did a little over 500w in 12 hours so time does matter as snowstorm noted.
I would also suggest that any watt hour capacity evaluations would be done with a Kilowatt Meter attached to the AC port. The wattage used displayed on the main screen is not exact and can be off at times which will skew your calculations. The wattage output displayed on the main screen is also the amount of output but does not add in the watts used to make the electrical output. The Inverter and DC ports consume electrical power just to generate the correct electrical output and this does not appear on the meter.
Larger loads and a Kill-a-Watt will give you better results. When I ran capacity tests on my refurbished EB240 and EB150 I used a small space heater plugged into the Kill-a-Watt and one of the AC plugs. The space heater started out at less than 400w but ramped up to 700w.
The problem with the Kill-a-Watt I used is it doesn’t save the read-out when the battery is drained. I used a Wyze cam set to time-lapse to record the results.
Don’t know if you have already completed a full power cycle on your sogen, drain unit until it automatically shuts off (10-11%), then recharge it to 100% to help calibrate the unit. I had power available issues before learning this, myself. After a full power cycle, i have not had anymore issues. Hope this helps!