SharePoint 2013: Unable to create or modify a list item. "Server was unable to save the form at this time" error

Brief Description:

A client recently reported an error message was being received when they were attempting to create a new list item or modify an existing list item.

Error Message:

"The server was unable to save the form at this time.  Please try again."

Additional Details:

The issue was reported as an entire team having the issue and it appeared to be contained to a single list.  They had previously been able to add or change items in this list.  The team reported that after they relocated to a new physical area, they were unable to modify the list.  This turned out to be a red herring.  I was thinking it might be something with the browser on their new machines, but that wasn't the case.

Troubleshooting:

• Confirmed this was not occurring on other sites or other lists.
• I was able to create new test items on the list and modify items on the list successfully.
• Confirmed the team could create new test items (with just test info).
• Copied the list to our test environment using Sharegate and attempted to create the exact same record that was causing the issue for that team.  I put in the exact same data and I was able to recreate it.

They were typing in much of the info into the list, but there was one multi-line text field where they were pasting information in from their ticketing system.  This seemed to be the only difference between creating the test records that were successful and the unsuccessful records.  I did try pasting in data from that system in testing, but I just grabbed something from the ticket, and I didn't receive the error.  It wasn't until I used the exact few lines that they were using that it was re-creatable.

In looking closer at what was being pasted in, it appeared to be just text.  I changed the column type to plain text (from rich text), but this did not help.  I noticed some unusual arrow characters in the text. But when I had pasted into SharePoint, they did not appear.  I removed those characters prior to copying when I pasted it in, everything saved correctly!

It appears that those may have been some hidden control characters... if anyone knows for sure, please let me know.

Other related info:

During my research on this error, I found several other people had been experiencing it, but on a much larger scale and they had resolved those cases with and some of these approaches: IIS reset, removal of browser add-ons, restart the SharePoint Search Hosting Controller service.  If you are experiencing this issue and it doesn't appear to be caused by unusual characters being pasted into the list, you may find some answers in this article: Technet: The server was unable to save the form at this time. Please try again.