@Patrick_Clough, I’m moving this to the Bugs category. In the meantime, try updating your safari webdriver.
@devalex88 There is something strange going on here. Please read the foregoing, then please consider my further points here…
The key error lines from Patrick’s dump seem to be:
And …
The first line seems to be the “new normal” if an alert is present and acceptAlert() has issues - but why? The latter message seems weird to me. I don’t have access to Safari so I can’t investigate further.
When I run this code (note WITHOUT an acceptAlert()
WebUI.executeJavaScript('alert("Hello World")', null)
I see the alert then get these two lines:
Unable to execute JavaScript. (Root cause: com.kms.katalon.core.exception.StepFailedException: Unable to execute JavaScript. ...
And then as you would expect…
Caused by: org.openqa.selenium.UnhandledAlertException: Dismissed user prompt dialog: Hello World:
Can you explain why Katalon/Webdriver is responding with “Unable to execute JavaScript”? There is no Javascript beyond the call to alert() so what JavaScript is it unable to execute? 
I am now of the opinion that my assumptions about execution of JavaScript while the browser is “paused” on an alert maybe ill-founded. I’m not completely certain but I thought I had done that in the past and recently found it was not working. That is what caused me to write this tip:
When I wrote the tip I thought it made some sense that the browser couldn’t run more JavaScript… but that’s the same message here with one line of JS it certainly has run.
If you can find out why this is happening and solve the safari issue at the same time I’ll make sure we sing your praises from rooftops all round the world 