I was using Nintex o365 workflow on the migrated site from SharePoint on prem to SharePoint online. When the workflow started on the item, it was showing the following message,

Error: Activity in progress. Retrying last request. Next attempt scheduled after <time>. Details of last request: HTTP NotFound to https://<tenant&gt;.sharepoint.com/sites/<siteurl>/_api/web/lists(guid'<listguid>’)/Items(<itemguid>)?%24select=ID%2CTitle

After a while, i found out that I need to activiate feature “Workflows can use app permissions”. Even Nintex prompt to enable this feature, when you are on nintex workflow desinger, it was my bad i ignored this message. As developer only notice error or exception 🙂