Looks like module is working again in rakudo 2018.10.

> perl6 --version
This is Rakudo Star version 2018.10 built on MoarVM version 2018.10
implementing Perl 6.c.

One issue found:
bin/daemonize exec dies with:

> perl6 -Ilib/ bin/daemonize sleep 10
No such method 'cando' for invocant of type 'Callable'
  in block <unit> at bin/daemonize line 4

t/01-lockfiles.t ............................. ok   
t/02-daemon-creates-pidfile-and-cleans-up.t ..     # Failed test 'Still alive'
    # at t/02-daemon-creates-pidfile-and-cleans-up.t line 16
    # Looks like you failed 1 test of 3
t/02-daemon-creates-pidfile-and-cleans-up.t .. 1/? # Failed test 'Pidlock files actually working for daemon and are removed afterwards'
# at t/02-daemon-creates-pidfile-and-cleans-up.t line 5
# Looks like you failed 1 test of 1
t/02-daemon-creates-pidfile-and-cleans-up.t .. Dubious, test returned 1 (wstat 256, 0x100)
Failed 1/1 subtests 
t/03-repeated-daemon-doesnt-finish.t .........     # Failed test 'Daemon still alive'
    # at t/03-repeated-daemon-doesnt-finish.t line 11
    # Failed test 'Daemon is restarted'
    # at t/03-repeated-daemon-doesnt-finish.t line 13
No valid lockfile
  in sub terminate-process-group-from-file at /home/alex/git/p6-UNIX-Daemonize/lib/UNIX/Daemonize.pm6 (UNIX::Daemonize) line 110
  in block <unit> at t/03-repeated-daemon-doesnt-finish.t line 15

t/03-repeated-daemon-doesnt-finish.t ......... Dubious, test returned 2 (wstat 512, 0x200)
No subtests run 
t/04-creating-second-daemon.t ................     # Failed test at t/04-creating-second-daemon.t line 11
    # Looks like you failed 1 test of 2
t/04-creating-second-daemon.t ................ 1/? # Failed test 'Won't create second daemon'
# at t/04-creating-second-daemon.t line 5
# Looks like you failed 1 test of 1
t/04-creating-second-daemon.t ................ Dubious, test returned 1 (wstat 256, 0x100)
Failed 1/1 subtests 

Test Summary Report
-------------------
t/02-daemon-creates-pidfile-and-cleans-up.t (Wstat: 256 Tests: 1 Failed: 1)
  Failed test:  1
  Non-zero exit status: 1
t/03-repeated-daemon-doesnt-finish.t       (Wstat: 512 Tests: 0 Failed: 0)
  Non-zero exit status: 2
  Parse errors: No plan found in TAP output
t/04-creating-second-daemon.t              (Wstat: 256 Tests: 1 Failed: 1)
  Failed test:  1
  Non-zero exit status: 1
Files=4, Tests=3, 12 wallclock secs ( 0.03 usr  0.00 sys +  2.65 cusr  0.23 csys =  2.91 CPU)
Result: FAIL

Seems like it worked fine on 2017.09 but on HEAD it fails.

This is Rakudo version 2017.09-481-g312cac786 built on MoarVM version 2017.09.1-609-g1a9be0ad
implementing Perl 6.c.

marlik@noutbook:/var/www/mydaemon$ zef --install-to=inst#/home/marlik/.perl6 install UNIX::Daemonize
===> Searching for: UNIX::Daemonize
===> Searching for missing dependencies: Test::When, Test::META
===> Searching for missing dependencies: META6, URI
===> Searching for missing dependencies: JSON::Class, JSON::Fast
===> Searching for missing dependencies: JSON::Marshal, JSON::Unmarshal
===> Searching for missing dependencies: JSON::Name
===> Testing: Test::When:ver<1.001008>
===> Testing [OK] for Test::When:ver<1.001008>
===> Testing: JSON::Fast:ver<0.9.8>
===> Testing [OK] for JSON::Fast:ver<0.9.8>
===> Testing: JSON::Name:ver<0.0.2>:authgithub:jonathanstowe
===> Testing [OK] for JSON::Name:ver<0.0.2>:authgithub:jonathanstowe
===> Testing: JSON::Marshal:ver<0.0.13>:authgithub:jonathanstowe
===> Testing [OK] for JSON::Marshal:ver<0.0.13>:authgithub:jonathanstowe
===> Testing: JSON::Unmarshal:ver<0.08>
===> Testing [OK] for JSON::Unmarshal:ver<0.08>
===> Testing: JSON::Class:ver<0.0.10>:authgithub:jonathanstowe
===> Testing [OK] for JSON::Class:ver<0.0.10>:authgithub:jonathanstowe
===> Testing: META6:ver<0.0.18>:authgithub:jonathanstowe
===> Testing [OK] for META6:ver<0.0.18>:authgithub:jonathanstowe
===> Testing: URI:ver<0.1.4>
===> Testing [OK] for URI:ver<0.1.4>
===> Testing: Test::META:ver<0.0.13>:authgithub:jonathanstowe

the following may make some diagnostics from the module itself

===> Testing [OK] for Test::META:ver<0.0.13>:authgithub:jonathanstowe
===> Testing: UNIX::Daemonize:ver<0.0.4>
# Failed test 'Lockfile should be removed'
# at t/02-daemon-creates-pidfile-and-cleans-up.t line 19
# Looks like you failed 1 test of 3

Failed test 'Pidlock files actually working for daemon and are removed afterwards'

at t/02-daemon-creates-pidfile-and-cleans-up.t line 5

Looks like you failed 1 test of 1

Valid lockfile exists
in sub lockfile-create at /home/marlik/.zef/store/p6-UNIX-Daemonize.git/044a39528a21da78010f26f49d39b24aaf233450/lib/UNIX/Daemonize.pm6 (UNIX::Daemonize) line 164
in sub daemonize at /home/marlik/.zef/store/p6-UNIX-Daemonize.git/044a39528a21da78010f26f49d39b24aaf233450/lib/UNIX/Daemonize.pm6 (UNIX::Daemonize) line 35
in block at t/04-creating-second-daemon.t line 9

# Failed test at t/04-creating-second-daemon.t line 13
# Looks like you failed 1 test of 2

Failed test 'Won't create second daemon'

at t/04-creating-second-daemon.t line 5

Looks like you failed 1 test of 1

===> Testing [FAIL]: UNIX::Daemonize:ver<0.0.4>
Aborting due to test failure: UNIX::Daemonize:ver<0.0.4> (use --force-test to override)
in code at /opt/rakudo-pkg/share/perl6/sources/0061125F96D1E60B6E3B0001A4CB4D4188DF4869 (Zef::Client) line 375
in method test at /opt/rakudo-pkg/share/perl6/sources/0061125F96D1E60B6E3B0001A4CB4D4188DF4869 (Zef::Client) line 353
in code at /opt/rakudo-pkg/share/perl6/sources/0061125F96D1E60B6E3B0001A4CB4D4188DF4869 (Zef::Client) line 530
in sub at /opt/rakudo-pkg/share/perl6/sources/0061125F96D1E60B6E3B0001A4CB4D4188DF4869 (Zef::Client) line 527
in method install at /opt/rakudo-pkg/share/perl6/sources/0061125F96D1E60B6E3B0001A4CB4D4188DF4869 (Zef::Client) line 633
in sub MAIN at /opt/rakudo-pkg/share/perl6/sources/C360CEB3AF792C33F65155FA82FDB7AB4467EC82 (Zef::CLI) line 152
in block at /opt/rakudo-pkg/share/perl6/resources/1063D2A135456C8AB42D605E20DBCF9E4A1C9F3B line 1
in sub MAIN at /opt/rakudo-pkg/bin/zef line 2
in block at /opt/rakudo-pkg/bin/zef line 2

[UNIX::Daemonize] # Failed test 'Lockfile should be removed'
[UNIX::Daemonize] # at t/02-daemon-creates-pidfile-and-cleans-up.t line 19
[UNIX::Daemonize] # You failed 1 test of 3
[UNIX::Daemonize] # Failed test 'Pidlock files actually working for daemon and are removed afterwards'
[UNIX::Daemonize] # at t/02-daemon-creates-pidfile-and-cleans-up.t line 5
[UNIX::Daemonize] # You failed 1 test of 1
[UNIX::Daemonize] Valid lockfile exists
[UNIX::Daemonize] in sub lockfile-create at /root/.zef/store/p6-UNIX-Daemonize.git/044a39528a21da78010f26f49d39b24aaf233450/lib/UNIX/Daemonize.pm6 (UNIX::Daemonize) line 164
[UNIX::Daemonize] in sub daemonize at /root/.zef/store/p6-UNIX-Daemonize.git/044a39528a21da78010f26f49d39b24aaf233450/lib/UNIX/Daemonize.pm6 (UNIX::Daemonize) line 35
[UNIX::Daemonize] in block at t/04-creating-second-daemon.t line 9
[UNIX::Daemonize] # Failed test at t/04-creating-second-daemon.t line 13
[UNIX::Daemonize] # You failed 1 test of 2
[UNIX::Daemonize] # Failed test 'Won't create second daemon'
[UNIX::Daemonize] # at t/04-creating-second-daemon.t line 5
[UNIX::Daemonize] # You failed 1 test of 1
===> Testing [FAIL]: UNIX::Daemonize:ver<0.0.4>
Aborting due to test failure: UNIX::Daemonize:ver<0.0.4> (use --force-test to override)
[frank@FedoraDT fetchmail]$ raku --version
This is Rakudo version 2020.07 built on MoarVM version 2020.07
implementing Raku 6.d.