Xpages - JS code fails to execute when clicked via a button - xpages

Question

I have a strange issue, where I have a simple javascript button, that call's 1 function to write some document history and replace the value of one field. It then does a partial update of a container div ID.
This button works fine when accessed via the UK, however when used by Swiss colleagues, the button is doing nothing.
I have in 1 instance, witnessed it not working for 1 user, only for it to suddenly work later in the day, so I'm stumped as to what the issue may be.
Button Code
<xp:button id="btnProceed" styleClass="btn btn-primary" value="Proceed">
<xp:this.disabled><![CDATA[#{javascript:try{
if (getComponent("chkConfirmed").getValue() == "false") {
return true;
} else {
return false;
}
}catch(e){
openLogBean.addError(e,this);
}
}]]></xp:this.disabled>
<xp:eventHandler event="onclick" submit="true" refreshMode="partial"
refreshId="contentWhiteBackground">
<xp:this.action><![CDATA[#{javascript:var dt = new Date();
var arrHistory:array = AddIndepConfirmationHistoryItem(currentDocument, dt, "Confirmed understanding of the opening guidance", userBean.displayName);
document1.replaceItemValue("showIntroduction", "2");
document1.save();
}]]></xp:this.action>
</xp:eventHandler></xp:button>
Called code
Sub AddIndepConfirmationHistoryItem(confdoc As NotesDocument, dt As Variant, action As String, usrname As String)
Dim hlist As StringList
If Len(confdoc.History(0)) = 0 Then
confdoc.History = IndepConfirmationHistoryItem(dt, action, usrname)
Else
Set hlist = New StringList(confdoc.History, "")
Call hlist.Append(IndepConfirmationHistoryItem(dt, action, usrname))
confdoc.History = hlist.Items
End If
End Sub
EDIT:
function AddIndepConfirmationHistoryItem(doc, dt, action, username){
var ArrDocHistory:array = doc.getItemValueArray("History");
var dateTimeFormat = new java.text.SimpleDateFormat("dd/MM/yyyy kk:mm");
var dateTimeString = dateTimeFormat.format(dt);
if(ArrDocHistory.length < 1){
// This should always return an object as it is created when an objectives document is first
// created but do this check to be safe and create an array if for some reason it doesnt exist
ArrDocHistory = [dateTimeString+"|"+action+"|"+username];
}else{
// append new value to the array
ArrDocHistory.push(dateTimeString+"|"+action+"|"+username);
}
doc.replaceItemValue("History",ArrDocHistory);
doc.replaceItemValue("LastUpdatedByName",username);
doc.replaceItemValue("LastUpdatedDate",dt);
//doc.Save();
}