Thanks for testing. I could not reproduce the error message you received. It is a custom response check that I implemented but it should not have been triggered. I do not receive it when following the workflow you described.
Let me say that I added some pages in the meantime, such that my original page numbers are not 42 instead of 40 for the pageorder and 43 instead of 41 for question "CH06" (46 instead of 43 for question "CH07" respectively).
For me, this worked as of now: starting on page 20 in debug mode, then skipping from there to page 42 using the orange bar on top. Leaving the two input fields blank and clicking 'next' then leads to the described issue. Does that work for you, too?
Thanks for hinting at the new feature, I will try processing the answers on the same page using PHP code wherever possible. Unfortunately, moving the PHP code to the end of previous pages does not work for pages 41 'weightlog' and 42 'pageorder' in particular, because I need to jump to these pages from different locations in the questionnaire depending on the randomization.
Would you recommend duplicating the PHP code on page 41 and 42 and moving it to the ends of these page locations, from where I currently jump?