I was able to see the problem with your file.I expect that there's some sort of problem with how the placement of content is defined in the original file.
I imposed it 1up using an Automatic press sheet size and .5" margins to correct the problem. Please escalate to the hotline so a developer can take a look to see if there's anything we should be doing in imposition.
Before the 2up imposition do the 1up imposition with the following settings
I changed my settings to mirror yours and everything is still working as expected.
It may be something with the file itself. Can you escalate to the hotline and also send me a link to the file via private message?
I added a node to save the file after the resize, and the input file looks fine. My resize settings are exactly like yours. Here are my imposition settings:
I just tried this (I added line marks to mark the trim box in the original document). It is working as expected.
I used the following Resize settings
Running FreeFlowCore 126.96.36.199. I have a workflow where I resize the trim box to add 1/4" to the top and bottom of the page, then impose with 2up Flip left on a web sheet. The image on the left is not placed similar to the one on the right. This only appears to happen if I resize the page.