do you have any update item action down the until flexi task resp. commit action?

The only actions before the problematic ones were send notification actions.

I have now tried this on a new, manually created list, and the workflow functions properly.

have you created workflow in former case (when it failed) from template?

try to remove workflow created from template and create new one through export/import (XML). there are quite often reported issues with workflows created from list template.

When I created the list from the template I had to manually remove the original workflow from the list by going to Workflow Settings and making sure the workflow from the original list wasn't running on the new list.  Then I created the new one through export/import, and the problems I first described started happening.

would you mind to share screenshot of your workflow, at least up to action(s) that fail?

and config of failing flexi task?

just to get a picture what might get into a game

do you use (customized) nintex form for flexi task?

do you have any kind of customization on workflow task list? do you use the same workflow task list for both original and imported workflow?

See screenshots below.  These are from the new (non-template) list, but the workflow is identical to the one that broke.  There is no customized form on the flexi task, and no reminders or escalation.  When I was struggling with the first workflow, I tried changing the workflow task list to a new, empty task list, but it did not change the behavior.

ok, thanks.

to understand it a bit further:

- does it fail on very first flexi task (default branch) or does it fail just after state machine switch?

- does it fail on each of flexi tasks? - could you try to change default branch so that it goes directly to other flexi task?

- do you get notification from flexi task that task was created/assigned?

- have you checked workflow task list whether there is created task item?

- you mentioned it fails with commit either, where exactly have you placed it?

- do you run workflow manualy or is it triggered by create/change events?

some ideas what to try out

- ensure permissions are set correctly on list and task list

- run flexi task without lazy approval

- disable 'Create workflow status column' workflow setting (check the status column disappears from the list)

- try to add pause for action at the very beginning of workflow

- add a branch to SM without flexi task, just with state change, and make it default

In the original workflow it would fail on any flexi task, no matter how it was set up or where it was (in or before state machine).  I did get notifications from the failed flexi tasks, but they would be immediately followed, or even preceded, by the failure notices.  Task lists never showed items, which was weird.  I tried the commit action before state machine and it failed.  When testing the workflow I always started it manually, with full control permissions.  I did not try disabling the workflow status column. 

Thanks for the help trying to disentangle this, but I am going to give up on it.  I got an equivalent workflow running on a new list, so this broken one doesn't really matter.  Just confusing.