ADDITIONAL SYSTEM INFORMATION :
I have no reason to think this is in any way platform specific, but my system is:
java.version = 16.0.2
javafx.runtime.version = 16+8
os.name = Windows 10
os.arch = amd64
os.version = 10.0

A DESCRIPTION OF THE PROBLEM :
Until JDK 15, SimpleDateFormat would successfully parse date strings including the month September abbreviated as the 3 letters "Sep".
With JDK 16, this now fails with java.text.ParseException: Unparseable dateIt will parse 
September abbreviated as the 4 letters "Sept", but if the date string comes from third party software, for example the "expires" value in the header data for a cookie from a web browser, JDK 16 now fails where JDK 15 worked.
I have confirmed that this is still broken in JDK 17 & 18 early access versions.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Try to parse a date such as "Sat, 03 Sep 2022 15:42:22 GMT" using SimpleDateFormat("EEE, dd MMM yyyy HH:mm:ss")

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
java.version = 15
dateString = Sat, 03 Jan 2022 15:42:22 GMT
    date = Mon Jan 03 15:42:22 GMT 2022
    formatted date = Mon, 03 Jan 2022 15:42:22
dateString = Sat, 03 Feb 2022 15:42:22 GMT
    date = Thu Feb 03 15:42:22 GMT 2022
    formatted date = Thu, 03 Feb 2022 15:42:22
dateString = Sat, 03 Mar 2022 15:42:22 GMT
    date = Thu Mar 03 15:42:22 GMT 2022
    formatted date = Thu, 03 Mar 2022 15:42:22
dateString = Sat, 03 Apr 2022 15:42:22 GMT
    date = Sun Apr 03 15:42:22 BST 2022
    formatted date = Sun, 03 Apr 2022 15:42:22
dateString = Sat, 03 May 2022 15:42:22 GMT
    date = Tue May 03 15:42:22 BST 2022
    formatted date = Tue, 03 May 2022 15:42:22
dateString = Sat, 03 Jun 2022 15:42:22 GMT
    date = Fri Jun 03 15:42:22 BST 2022
    formatted date = Fri, 03 Jun 2022 15:42:22
dateString = Sat, 03 Jul 2022 15:42:22 GMT
    date = Sun Jul 03 15:42:22 BST 2022
    formatted date = Sun, 03 Jul 2022 15:42:22
dateString = Sat, 03 Aug 2022 15:42:22 GMT
    date = Wed Aug 03 15:42:22 BST 2022
    formatted date = Wed, 03 Aug 2022 15:42:22
dateString = Sat, 03 Sep 2022 15:42:22 GMT
    date = Sat Sep 03 15:42:22 BST 2022
    formatted date = Sat, 03 Sep 2022 15:42:22
dateString = Sat, 03 Oct 2022 15:42:22 GMT
    date = Mon Oct 03 15:42:22 BST 2022
    formatted date = Mon, 03 Oct 2022 15:42:22
dateString = Sat, 03 Nov 2022 15:42:22 GMT
    date = Thu Nov 03 15:42:22 GMT 2022
    formatted date = Thu, 03 Nov 2022 15:42:22
dateString = Sat, 03 Dec 2022 15:42:22 GMT
    date = Sat Dec 03 15:42:22 GMT 2022
    formatted date = Sat, 03 Dec 2022 15:42:22
dateString = Sat, 03 Sept 2022 15:42:22 GMT
    java.text.ParseException: Unparseable date: "Sat, 03 Sept 2022 15:42:22 GMT"
ACTUAL -
java.version = 16.0.2
dateString = Sat, 03 Jan 2022 15:42:22 GMT
    date = Mon Jan 03 15:42:22 GMT 2022
    formatted date = Mon, 03 Jan 2022 15:42:22
dateString = Sat, 03 Feb 2022 15:42:22 GMT
    date = Thu Feb 03 15:42:22 GMT 2022
    formatted date = Thu, 03 Feb 2022 15:42:22
dateString = Sat, 03 Mar 2022 15:42:22 GMT
    date = Thu Mar 03 15:42:22 GMT 2022
    formatted date = Thu, 03 Mar 2022 15:42:22
dateString = Sat, 03 Apr 2022 15:42:22 GMT
    date = Sun Apr 03 15:42:22 BST 2022
    formatted date = Sun, 03 Apr 2022 15:42:22
dateString = Sat, 03 May 2022 15:42:22 GMT
    date = Tue May 03 15:42:22 BST 2022
    formatted date = Tue, 03 May 2022 15:42:22
dateString = Sat, 03 Jun 2022 15:42:22 GMT
    date = Fri Jun 03 15:42:22 BST 2022
    formatted date = Fri, 03 Jun 2022 15:42:22
dateString = Sat, 03 Jul 2022 15:42:22 GMT
    date = Sun Jul 03 15:42:22 BST 2022
    formatted date = Sun, 03 Jul 2022 15:42:22
dateString = Sat, 03 Aug 2022 15:42:22 GMT
    date = Wed Aug 03 15:42:22 BST 2022
    formatted date = Wed, 03 Aug 2022 15:42:22
dateString = Sat, 03 Sep 2022 15:42:22 GMT
    java.text.ParseException: Unparseable date: "Sat, 03 Sep 2022 15:42:22 GMT"
dateString = Sat, 03 Oct 2022 15:42:22 GMT
    date = Mon Oct 03 15:42:22 BST 2022
    formatted date = Mon, 03 Oct 2022 15:42:22
dateString = Sat, 03 Nov 2022 15:42:22 GMT
    date = Thu Nov 03 15:42:22 GMT 2022
    formatted date = Thu, 03 Nov 2022 15:42:22
dateString = Sat, 03 Dec 2022 15:42:22 GMT
    date = Sat Dec 03 15:42:22 GMT 2022
    formatted date = Sat, 03 Dec 2022 15:42:22
dateString = Sat, 03 Sept 2022 15:42:22 GMT
    date = Sat Sep 03 15:42:22 BST 2022
    formatted date = Sat, 03 Sept 2022 15:42:22

Full stack trace:
java.text.ParseException: Unparseable date: "Sat, 03 Sep 2022 15:42:22 GMT"
at java.base/java.text.DateFormat.parse(DateFormat.java:396)
at dateparsingbug.DateParsingBug.main(DateParsingBug.java:38)

---------- BEGIN SOURCE ----------

import java.text.SimpleDateFormat;
import java.util.Date;

public class DateParsingBug {

/**
* @param args the command line arguments
*/
public static void main(String[] args) {
SimpleDateFormat TEST_DATE_AND_TIME_FORMAT = new SimpleDateFormat("EEE, dd MMM yyyy HH:mm:ss");
String[] monthNames = {
"Jan",
"Feb",
"Mar",
"Apr",
"May",
"Jun",
"Jul",
"Aug",
"Sep",
"Oct",
"Nov",
"Dec",
"Sept"
};

System.out.println("java.version = " + System.getProperty("java.version"));
for (String monthName: monthNames) {
try {
String dateString = "Sat, 03 " + monthName + " 2022 15:42:22 GMT";
System.out.println("dateString = " + dateString);
Date date = TEST_DATE_AND_TIME_FORMAT.parse(dateString);
System.out.println(" date = " + date);
System.out.println(" formatted date = " + TEST_DATE_AND_TIME_FORMAT.format(date));
} catch (Exception ex) {
System.out.println(" " + ex);
}
}
}
}
---------- END SOURCE ----------

FREQUENCY : always