Did you maybe remove a goal after some conversions were tracked?

No, we did not change a goal. I just checked: the goals did not change more than a week, but the visitor was registered today.

Does the error always occur?

Yes, the error appears every time. Restarting a web server and disabling plugins does not help.

@efedorov I'm not sure how this problem occurs. Could you check if applying following changes fixes the problem for you: https://github.com/piwik/piwik/compare/fixgoalvp#diff-e968bd8d9abc8cf8161a4c09567ddc52

@efedorov did you have time to check it? Would love to include a fix in next release if we can figure out the exact problem.

let's merge the fix if it's appropriate and could prevent an error in edge case? (as long as it doesn't hide a real issue...)