ADDITIONAL SYSTEM INFORMATION :
Tested on Windows and MacOS

A DESCRIPTION OF THE PROBLEM :
Using regex for natural language processing, tokenization, to find places between non-repeating punctuations and symbol characters now finds breaks between different whitespace characters.

REGRESSION : Last worked in version 8u251

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Results for 1st and 2nd regex patterns show different behavior for Java 8 vs Java 11 runtimes.
3rd and 4th patterns seem stable but should be equivalent.
Non alpha numeric, non - whitespace character not followed by the same character
In Java 11, the 1st pattern is now matching spaces and the 2nd is also matching alphanumeric 


EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Java HotSpot(TM) 64-Bit Server VM
Oracle Corporation
25.221-b11
Running Test
Text: aabcc<space><newline><newline><tab><tab><newline><space><newline><newline>..,;;

Pattern: ([^0-9a-z&&[^\s]])(?!\1)
	Index: 15, 16 Group: . Next Char: ,
	Index: 16, 17 Group: , Next Char: ;
	Index: 18, 19 Group: ; Next Char: 
Pattern: ([^0-9a-z&&[\s]])(?!\1)
	Index: 5, 6 Group: <space> Next Char: <newline>
	Index: 7, 8 Group: <newline> Next Char: <tab>
	Index: 9, 10 Group: <tab> Next Char: <newline>
	Index: 10, 11 Group: <newline> Next Char: <space>
	Index: 11, 12 Group: <space> Next Char: <newline>
	Index: 13, 14 Group: <newline> Next Char: .
Pattern: ([\S&&[\w]])(?!\1)
	Index: 1, 2 Group: a Next Char: b
	Index: 2, 3 Group: b Next Char: c
	Index: 4, 5 Group: c Next Char: <space>
Pattern: ([\S&&[\W]])(?!\1)
	Index: 15, 16 Group: . Next Char: ,
	Index: 16, 17 Group: , Next Char: ;
	Index: 18, 19 Group: ; Next Char: 

ACTUAL -
Java HotSpot(TM) 64-Bit Server VM
Oracle Corporation
11.0.7+8-LTS
Running Test
Text: aabcc<space><newline><newline><tab><tab><newline><space><newline><newline>..,;;

Pattern: ([^0-9a-z&&[^\s]])(?!\1)
	Index: 5, 6 Group: <space> Next Char: <newline>
	Index: 7, 8 Group: <newline> Next Char: <tab>
	Index: 9, 10 Group: <tab> Next Char: <newline>
	Index: 10, 11 Group: <newline> Next Char: <space>
	Index: 11, 12 Group: <space> Next Char: <newline>
	Index: 13, 14 Group: <newline> Next Char: .
	Index: 15, 16 Group: . Next Char: ,
	Index: 16, 17 Group: , Next Char: ;
	Index: 18, 19 Group: ; Next Char: 
Pattern: ([^0-9a-z&&[\s]])(?!\1)
	Index: 1, 2 Group: a Next Char: b
	Index: 2, 3 Group: b Next Char: c
	Index: 4, 5 Group: c Next Char: <space>
	Index: 5, 6 Group: <space> Next Char: <newline>
	Index: 7, 8 Group: <newline> Next Char: <tab>
	Index: 9, 10 Group: <tab> Next Char: <newline>
	Index: 10, 11 Group: <newline> Next Char: <space>
	Index: 11, 12 Group: <space> Next Char: <newline>
	Index: 13, 14 Group: <newline> Next Char: .
	Index: 15, 16 Group: . Next Char: ,
	Index: 16, 17 Group: , Next Char: ;
	Index: 18, 19 Group: ; Next Char: 
Pattern: ([\S&&[\w]])(?!\1)
	Index: 1, 2 Group: a Next Char: b
	Index: 2, 3 Group: b Next Char: c
	Index: 4, 5 Group: c Next Char: <space>
Pattern: ([\S&&[\W]])(?!\1)
	Index: 15, 16 Group: . Next Char: ,
	Index: 16, 17 Group: , Next Char: ;
	Index: 18, 19 Group: ; Next Char: 


---------- BEGIN SOURCE ----------
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class TestRegex {

	public static void main(String[] args) {
		System.out.println(System.getProperty("java.vm.name"));
		System.out.println(System.getProperty("java.vm.vendor"));
		System.out.println(System.getProperty("java.vm.version"));

		System.out.println("Running Test");
		String[] testRegex = new String[] { "([^0-9a-z&&[^\\s]])(?!\\1)", "([^0-9a-z&&[\\s]])(?!\\1)", "([\\S&&[\\w]])(?!\\1)", "([\\S&&[\\W]])(?!\\1)" };
		String text = "aabcc \n\n\t\t\n \n\n..,;;";
		System.out.println("Text: " + printable(text));
		System.out.println();
		for (String regex : testRegex) {
			Pattern pattern = Pattern.compile(regex, Pattern.CASE_INSENSITIVE);
			System.out.println("Pattern: " + pattern.pattern());
			Matcher m = pattern.matcher(text);
			while (m.find()) {
				System.out
						.println("\tIndex: " + m.start() + ", " + m.end() + " Group: " + printable(m.group()) + " Next Char: " + printable((m.end() < text.length() ? "" + text.charAt(m.end()) : "")));
			}
		}

	}

	public static String printable(String text) {
		text = text.replaceAll("\t", "<tab>");
		text = text.replaceAll("\n", "<newline>");
		text = text.replaceAll(" ", "<space>");
		return text;
	}

}
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Have to use the \S and \W character classes that also allow the underscore character, which is a loss of precision. 

FREQUENCY : always