When you choose to mark all as reviewed, your computer sends a message to iNat for each unreviewed observation remaining on the page, telling it to mark that observation as reviewed. This takes some amount of time, depending on how many observations need to be marked, the speed of your connection, the current load on iNat’s servers, etc.
Choosing to view more (or view more unreviewed) makes a fresh call to iNat asking for your search results, i.e. a refreshed version of page 1 of the results.
Choosing to skip to next page asks iNat for page 2 of your results, but these are not the “original page 2 results”, they’re the second page of a fresh call for your results. So if you are searching unreviewed observations (the default), and you marked 5 as reviewed on your first page of 30, asking for the next page doesn’t bring 31-60, it brings 36-65 (assuming no obs were added in the meantime). Observations 31-35 are on the new page 1.
The topic title says “go to next page”, but I assume the desired behavior is actually the view more function mentioned in the second paragraph of the original post.
Certainly there are ways to solve this problem, but simply making the call to view more before finishing the calls to mark as reviewed won’t work here – the “view more” page will still include the observations that haven’t yet been marked as reviewed.
Other topics about the flow and pagination of Identify:
https://forum.inaturalist.org/t/improve-flow-of-identify-mode/299
https://forum.inaturalist.org/t/identify-mode-page-break/11219