[Koha] Koha plack is not working

[Bedanta Borah]

I have installed koha on Ubuntu in VirtualBox. Following are my Koha Server
Information.

Server information Koha version:     18.11.03.000
OS version ('uname -a'):     Linux StaticStudy 4.15.0-46-generic #49-Ubuntu
SMP Wed Feb 6 09:33:07 UTC 2019 x86_64
Perl interpreter:     /usr/bin/perl
Perl version:     5.026001
Perl @INC:     /usr/share/koha/lib
/etc/perl
/usr/local/lib/x86_64-linux-gnu/perl/5.26.1
/usr/local/share/perl/5.26.1
/usr/lib/x86_64-linux-gnu/perl5/5.26
/usr/share/perl5
/usr/lib/x86_64-linux-gnu/perl/5.26
/usr/share/perl/5.26
/usr/local/lib/site_perl
/usr/lib/x86_64-linux-gnu/perl-base
MySQL version:     mysql Ver 14.14 Distrib 5.7.25, for Linux (x86_64) using
EditLine wrapper
Apache version:     Server version: Apache/2.4.29 (Ubuntu)
Memcached:     Servers: 127.0.0.1:11211 | Namespace: koha_library | Status:
running. | Config read from: koha-conf.xml
Zebra version:     Zebra 2.0.59 (C) 1994-2014, Index Data Zebra is free
software, covered by the GNU General Public License, and you are welcome to
change it and/or distribute copies of it under certain conditions. SHA1 ID:
c00bfddbf0f3608340d61298acc61dafb167f9b2 Using ICU
Date and time:     04/09/2019 09:12
Time zone:     Used: Asia/Kolkata | Config: Undefined | Environment (TZ):
Undefined

I try to start and eneble 'Plack' through following commands

sudo koha-plack --enable library
sudo koha-plack --start library
sudo service apache2 restart

Sometimes these commands work just fine and I get a significant boost in
speed. But after I turn off the virtual box and try to access it later,
koha stops working (nothing appears on 127.0.0.1:8080 & 8081) untill I
disable Plack through the following commands

sudo koha-plack --stop library
sudo koha-plack --disable library
sudo service apache2 restart. And the speed also reduces significantly.

Restarting Plack doesn't work.

Please guide me to solve this problem.