Sometimes we post links inside of updates in workfront. We've had a few issues where we'll post a link to a relevant workfront issue/task, and it'll include an extra space at the end of the link. This leads to the "This task no longer exists screen" in reality there's just an extra space in the url that needs to be removed.
I think that removing spaces from the end of URLs unless they are explicitly added with the create link button would be a good fix here. I'm also not sure what is causing the extra spaces to get inserted exactly. I don't think we're hitting space after posting the links so it could be a bug in the update text implementation but I haven't been able to reproduce it yet.