It sounds like you are using your co-workers layout in a different project. If they try your output on their machine, do they have the same issue?
Do you both have the same updates applied to RoboHelp?
Update 2 changed the layouts and after applying Update 2 you have to take fresh copies of the responsive layouts. Make sure you do that by clicking the Gallery button in your output dialog and do not use your browser to download them direct from Adobe's site. Despite several reminders that page is still showing it was last update Sept 2017, before the new layouts were created.
I realise that if your co-workers layout is working, logically it should work for you but nothing seems to be logical here so take a look at the above.
Are you sure it's not the whisky making things spin?
Oh I WISH it was the whiskey. Since I am the RH Whisperer for my team I am the only one who loaded up Service Pack 2 - or at least I hope so. So I sent my backup to a colleague who was able to publish and resolve the short term issue.
We use a custom layout that my supervisor built using Azure (I think - but it was one of the canned ones, anyway) and some tweaking. I would assume he will have to address this issue with having to re-take the layout and then do his tweaking again.
But for now, reinstalling to the older v of 2017 - and trying to get SP 1 in there. Thanks for the clues, Peter. You save my bacon every time.