Brandon here with the Webflow Customer Support Team!
I will be happy to help you with your question regarding getting columns to stack the way you want them.
Without a share link I cant say for 100% certain, but just based off how you have the info it is setup with horizontal flex and then changed to vertical Flex.
So the way you have it on desktop it is in a sense reading it as Image > text > Text > image > Image > Text
It is reading the content from left to right and then down to the next row and so forth.
What you can do is use the reverse order or specifically set the order of the elements by choosing how they show compared to first or last.
This has to do with Positioning elements within a Flex or Grid layout.
If you can provide the share link of your project I can show you.
Please let me know if you have any other questions,
~ Happy Designing ~