Editing some blocks on mobile deletes them on desktop view and vice versa.

I put some text in front of a colored rectangle in desktop. Looks good. I check it out on mobile, that rectangle is all the way at the bottom underneath all the text.
Okayyy.
So I moved it back up to the right place on mobile. Then I took a look at the desktop view again. Wha?? that rectangle has completely vanished on desktop! It hasn't been moved to the wrong place. It's just GONE. It's there on mobile but deleted on desktop. I've gone through this process three times this morning and it happens every time.

The same thing happened in reverse today. Yesterday, I put a colored rectangle underneath a sub-header at the top of the page, on desktop. But when I checked the mobile view today, that rectangle is completely gone there, nowhere to be seen, while it's still there on desktop.
And here's the weird thing: as I switch out of mobile view in the Squarespace editor, that rectangle flashes on the screen for just a split second, in the correct place, but the text of that sub-header is gone. Ghosts!

I tried to add the missing block on mobile, but it looks like there's no way to do that. I've been clicking all over the place and I can't get "add block" to show up.

Very frustrating. Hoping someone can help.

Hi,

What is site url?

This is the page where the rectangle disappeared on mobile:
https://www.womenspowervoice.com/private-sessions - behind the text "isn't it great to finally feel HEARD?"
When I went to take a look at it on mobile, I saw that rectangle was wayyy at the bottom for some reason. So I moved it up to where it belongs, but then it disappeared entirely.

At the bottom of that same page, I put a colored rectangle behind the text "You don't have to deal with this alone."  It shows up on mobile, but it has disappeared on desktop view.

I've already tried three times to fix this, without success.

Something just occurs to me in a "duh" moment. I wonder if it's possible to put a colored background on a text block, thus eliminating the need to coordinate the position of colored shapes with text blocks.
Going to try that.