Desktop Content not Automatically Carrying Over to Mobile Devices

I've had continuing problems with random parts of my desktop design not carrying over to the mobile devices, I'm talking here mostly about text elements. By default I'd assume they'd carry over even if the mobile sections for that text element is blank but that doesn't seem to always be the case.

I often have to go into the mobile settings for those missing text elements and sure enough the tablet and/or phone sections are blank...once I correct that the problem, of course, goes away.

My question is basically WHY this is happening? I assume the default behavior in Divi is to carry all text elements over to mobile without changes unless specified - what would interfere with that?

One thought I had is that maybe it happens when you EDIT a pre-existing piece of text content on your desktop site that it doesn't continue to carry over those changes and instead keeps the two mobile settings areas (for tablet and for phone) blank as before? Just an idea?