Please help us help you and fill where relevant:
Your LimeSurvey version: 3.28.8+220426

Getting this error when we try to Clean and Exit a Survey:
survey.js:420 Uncaught TypeError: Cannot read properties of undefined (reading 'submitter')
    at HTMLDocument.<anonymous> (survey.js:420:39)
    at HTMLDocument.dispatch (jquery-3.5.1.min.js:2:43090)
    at HTMLDocument.v.handle (jquery-3.5.1.min.js:2:41074)
    at Object.trigger (jquery-3.5.1.min.js:2:71513)
    at HTMLFormElement.<anonymous> (jquery-3.5.1.min.js:2:72108)
    at Function.each (jquery-3.5.1.min.js:2:2976)
    at s.fn.init.each (jquery-3.5.1.min.js:2:1454)
    at s.fn.init.trigger (jquery-3.5.1.min.js:2:72084)
    at s.fn.init.s.fn.<computed> [as submit] (jquery-migrate-3.3.2.min.js:2:8557)
    at HTMLButtonElement.<anonymous> (survey.js:305:34)
(anonymous) @ survey.js:420
dispatch @ jquery-3.5.1.min.js:2
v.handle @ jquery-3.5.1.min.js:2
trigger @ jquery-3.5.1.min.js:2
(anonymous) @ jquery-3.5.1.min.js:2
each @ jquery-3.5.1.min.js:2
each @ jquery-3.5.1.min.js:2
trigger @ jquery-3.5.1.min.js:2
s.fn.<computed> @ jquery-migrate-3.3.2.min.js:2
(anonymous) @ survey.js:305
dispatch @ jquery-3.5.1.min.js:2
v.handle @ jquery-3.5.1.min.js:2

Which Survey theme is used? If custom, try to test with a standard theme an see what happens.

It's a original theme, vanilla.

On my installation, Vanilla doesn't show the "Clean and exit" option at all. How did you activate it? I couldn't find a way to do so.

Hi.

Thank you for your reply, you have to have a second question group to advance in order for that button to appear.
Also, keep in mind that you have to set Settings > Notifications and data > Participant may save and resume later and activate the survey.

you have to have a second question group to advance in order for that button to appear.

Ok, this could be it.

Also, keep in mind that you have to set Settings > Notifications and data > Participant may save and resume later and activate the survey.

Hmmm, this doesn't make sense to me.

You can try this issue at this address:
inqueritos.up.pt/index.php?r=survey/index&sid=211649

Thank you in advance.

I tried it and a modal opens:

Por favor, confirmar: Sair e limpar inquérito?

When I click on OK, nothing happens. No error message, nothing.

There is a JavaScript error but I'm on my phone so can't follow up right now.

Hi.

That's right, that's the problem.
And you'll probably get the JS error after enabling debug on your browser.