ADDITIONAL SYSTEM INFORMATION :
Linux 64-bit. Originally discovered with OpenJDK 11.0.2, but I can reproduce it with the tip of http://hg.openjdk.java.net/jdk-updates/jdk12u/

A DESCRIPTION OF THE PROBLEM :
The TLSv1.3 spec has this to say about the allowed length of TLSInnerPlaintext:

   The presence of padding does not change the overall record size
   limitations - the full encoded TLSInnerPlaintext MUST NOT exceed 2^14
   + 1 octets.  If the maximum fragment length is reduced, as for
   example by the max_fragment_length extension from [RFC6066], then the
   reduced limit applies to the full plaintext, including the content
   type and padding.

However, t13Encrypt in src/java.base/share/classes/sun/security/ssl/OutputRecord.java will always append 16 padding bytes to the fragment, without taking into account its original size:

    private static final class T13PaddingHolder {
        private static final byte[] zeros = new byte[16];
    }

    private long t13Encrypt(
            SSLWriteCipher encCipher, byte contentType, int headerSize) {
        if (!encCipher.isNullCipher()) {
            // inner plaintext
            write(contentType);
            write(T13PaddingHolder.zeros, 0, T13PaddingHolder.zeros.length);
        }
        ...

This causes trouble with TLSv1.3 servers because we set Record.maxDataSize to 2^14, and so the added 1 + 16 bytes may cause the resulting TLSInnerPlaintext to go over the length limit.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Compile and run Test.java

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
The test TLSv1.3 server page at https://tls13.crypto.mozilla.org/ should be printed to console.
ACTUAL -
https://tls13.crypto.mozilla.org/ returns a "record_overflow" error.

---------- BEGIN SOURCE ----------
import javax.net.ssl.HttpsURLConnection;
import java.net.URL;
import java.io.*;
import java.nio.*;
import java.nio.charset.StandardCharsets;
import java.nio.file.*;

public class Test {
    public static void main(String[] args) throws Exception {
        StringBuilder data = new StringBuilder();
        data.append("----abc\r\n")
            .append("Content-Disposition: form-data; name=\"json_file\"; filename=\"test.json\"\r\n")
            .append("Content-Type: application/octet-stream\r\n")
            .append("\r\n");
        for (int i = 0; i < 325717; i++)
            data.append("a");
        data.append("----abc--");
        URL url = new URL("https://tls13.crypto.mozilla.org/");
        HttpsURLConnection connection = (HttpsURLConnection) url.openConnection();
        connection.setRequestMethod("POST");
        connection.setDoInput(true);
        connection.setDoOutput(true);
        connection.setRequestProperty("Content-Type", "multipart/form-data; boundary=--abc");
        OutputStreamWriter osw = new OutputStreamWriter(connection.getOutputStream());
        osw.write(data.toString());
        osw.flush();
        osw.close();
        BufferedReader br = new BufferedReader(new InputStreamReader(connection.getInputStream()));
        String line;
        while((line = br.readLine()) != null) {
            System.out.println(line);
        }
    }
}
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Disabling TLSv1.3 support by setting jdk.tls.client.protocols="TLSv1,TLSv1.1,TLSv1.2"