jlink does not create reproducible builds on different servers

ADDITIONAL SYSTEM INFORMATION :
Ubuntu 18.04
JDK 15 Build 36 (2020/8/11)
JDK 16 Build 13 (2020/8/26)

A DESCRIPTION OF THE PROBLEM :
Calling (the exact same) jlink with the exact same parameters on different machines and even folder results different output.


STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
JDK15:

    $ mkdir jdk-15a jdk-15b
    $ tar xzf openjdk-15_linux-x64_bin.tar.gz --directory jdk-15a/
    $ tar xzf openjdk-15_linux-x64_bin.tar.gz --directory jdk-15b/
    $ jdk-15a/jdk-15/bin/jlink --compress=1 --module-path jdk-15a/jdk-15/jmods --add-modules java.base,jdk.management,jdk.unsupported,jdk.charsets --output output01
    $ jdk-15b/jdk-15/bin/jlink --compress=1 --module-path jdk-15b/jdk-15/jmods --add-modules java.base,jdk.management,jdk.unsupported,jdk.charsets --output output02
    $ md5sum output*/lib/modules
    9ae5ae63df59593a0892c5ed411d7e59 output01/lib/modules
    24b4af31553670799ab286ad1186329e output02/lib/modules

JDK16:

    $ mkdir jdk-16a jdk-16b
    $ tar xzf openjdk-16-ea+13_linux-x64_bin.tar.gz --directory jdk-16a/
    $ tar xzf openjdk-16-ea+13_linux-x64_bin.tar.gz --directory jdk-16b/
    $ jdk-16a/jdk-16/bin/jlink --compress=1 --module-path jdk-16a/jdk-16/jmods --add-modules java.base,jdk.management,jdk.unsupported,jdk.charsets --output output01
    $ jdk-16b/jdk-16/bin/jlink --compress=1 --module-path jdk-16b/jdk-16/jmods --add-modules java.base,jdk.management,jdk.unsupported,jdk.charsets --output output02
    $ md5sum output*/lib/modules
    266b05c93ad3858757ec5f194bc7c019 output01/lib/modules
    e27a144d62605719bd8017c75e6aca69 output02/lib/modules


EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Same checksum for both lib/modules file.
ACTUAL -
Different cheksums for the lib/modules file.

FREQUENCY : always