So this post describes how to open the previous version of a workflow: How to restore/open an old version of my workflow.
When I click the "Open" icon I see the list of workflows as in the post. When I click on the + icon next to some of the workflows, I get a list of versions to choose from, but not for others. When I click the + icon next to the one I'm trying to work with, the + icon changes to a -, but no other action occurs. A list of previous versions does not appear. It seems that I'm getting a version list for those items that only have a few versions (e.g. maybe up to 7?), but that I'm not seeing the versions for workflows for more versions (e.g. the one I'm working with has 35 versions).
Any suggestions on what to check or try here?
try to navigate to <siteURL>/NintexWorkflows library
and check to see whether you have enabled versioning on this library
in the library you should see a folder for each workflow within the site. navigate to a respective folder (eg. one for which you do not version history ion designer).
in there you should see 2 or 3 files, check for one of them whether version history is maintained (they all should be at the same version number)