Just got the client's feedback: Survey is running fine!
Thank you all so much for the awesome support!

The real reason for this error is a second call (caused by the browser requesting the favicon), which is not properly handled by LimeSurvey. The following commit fixes the issue:

github.com/LimeSurvey/LimeSurvey/commit/...a10da0944928e2114fe4

See also bugs.limesurvey.org/view.php?id=15212

This took us so long to fix because the call does not usually show up in the developer console and every browser software requests it at a different time and we were not able to reproduce with recent browser versions.

c_schmitz wrote: The real reason for this error is a second call (caused by the browser requesting the favicon), which is not properly handled by LimeSurvey.

How do you come to that conclusion?

The case here is a running LS 3.17.5+190604 with a closed corporate user base with IE11/Win8.1 . The code changed with the missing ICO validation was done way later.


Changing the session name from the default to a unique one seemed to have fixed the issue here.
That wouldn't help when the missing ICO validation where in place.

jelo wrote: How do you come to that conclusion?

The case here is a running LS 3.17.5+190604 with a closed corporate user base with IE11/Win8.1 . The code changed with the missing ICO validation was done way later.


Changing the session name from the default to a unique one seemed to have fixed the issue here.
That wouldn't help when the missing ICO validation where in place.

I guess it‘s because we also opened a support ticket and our developer provided some extra information

However, LS will be a bit more stable with this commit.

Thank you all!

FlowinBeatz wrote: I guess it‘s because we also opened a support ticket and our developer provided some extra information

We are beyond guessing. I trust your statement about running version "LS 3.17.5+190604". That information rules out certain bugs which were introduced later.
Feel free to post the extra information from your developer here.

True, the bug with the favicon was introduced in 3.17.10+190821.