30psi is MUCH too high for a 4" wide tire. The label on the tire is indicating the MAXIMUM pressure, not the ideal pressure. I run about 10psi in my fat bike tires in the summer, lower in the winter for snow. If I were riding on the road only I might go up to 15 psi. 30 psi is insane and pretty much completely negates the advantages of having big fat tires. Soft tires are the whole reason for fat bikes - allows flotation on soft surfaces and absorbs small obstacles and irregularities - and soft tires will, as mentioned above, be less prone to punctures.
The only drawback to having low pressure is the tires will roll more slowly or take more effort to roll at your desired speed, but with an E-bike this is not an issue. For the love of your clients, PLEASE run those tires at lower pressure.