Ok, I was confused because I thought you were talking about Log Insight.
You might check, if you're in linked mode with multiple vCenters, that you're connected to the right one. Although events will show combined, they'll only be exported in the right instance. If that's still not working, try from PowerCLI with
Get-VIEvent -Start <date> -Finish 0<date> | Export-CSV .path/to/file.csv -NoTypeInformation -UseCulture
And see if that exports them. In a test I did in my lab, this did export all those events, including warnings and errors.