
Hi @Raymund Concon ,
- Are workflows for the same list item being triggered at the same time? This may cause conflict.
- Did you repost the workflow and still get the same error on startup? Does it happen in all workflows? Strat workflow with other account instead of system account and compare the results.
- Deactivate and re-activate the Workflows feature in Site collection features and check again.
- Clear the SharePoint Designer cache.
- Clear the SharePoint Designer login credentials.
- Have you recently made a .NET security update, check it and refer to the article to get it working after the update. (As the workaround mentioned in the article, this updated solution is to add some types in the web.config file on the SharePoint server.)
Reference: SharePoint workflows stop working after you install .NET security updates for CVE-2018-8421 - You will need to check the ULS log to find error message which may be related to this issue.
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