How to fix 'AH00992: ajp_read_header: ajp_ilink_receive failed' apache proxy error with glassfish server?

Question

Apache server is configure as proxy to Glassfish server. A Vaadin application has been deployed on the Glassfish sever. Application loading fails with CSS. Is it a problem with Apache configuration or Glassfish application/configuration ?

The system is configure with Apache 2.4 and Glassfish 5. The application is built with Vaadin 6.8 Glassfih has been confgured with ajp connector.

Virtual host configuration:

<VirtualHost *:443>
...
  SSLEngine on
  SSLCipherSuite HIGH:MEDIUM:!SSLv3:!kRSA
  SSLProtocol All -SSLv3
  SSLHonorCipherOrder On
  SSLCompression off
  SSLCertificateFile /etc/ssl/private/cert.pem
  SSLCertificateKeyFile /etc/ssl/private/privkey.pem
  SSLCertificateChainFile /etc/ssl/private/ca-crt.pem
<IfModule setenvif_module>
  BrowserMatch ".*MSIE.*" nokeepalive ssl-unclean-shutdown downgrade-1.0 force-response-1.0
</IfModule>
...
<IfModule rewrite_module>
    RewriteEngine On
#    LogLevel alert rewrite:trace3
    RewriteRule ^/api/(.*)$ /api/$1 [NC,PT]
    RewriteRule ^/myapp$ /myapp [NC,PT]
    RewriteRule ^/myapp/(.*)$ /myapp/$1 [NC,PT]
    RewriteRule ^(.*) /office [PT,L]
</IfModule>
...
<IfModule proxy_module>
   <Proxy *>
     AddDefaultCharset Off
     Order deny,allow
     Allow from all
   </Proxy>

<IfModule proxy_ajp_module>
  ProxyPass /myapp ajp://localhost:8009/myapp timeout=60
</IfModule>
</IfModule>
</VirtualHost>

Apache error_log shows following errors:

[Fri Aug 16 22:08:18.228731 2019] [proxy_ajp:error] [pid 3629:tid 140277591308032] (70014)End of file found: AH01030: ajp_ilink_receive() can't receive header
[Fri Aug 16 22:08:18.228764 2019] [proxy_ajp:error] [pid 3629:tid 140277591308032] [client 192.168.34.1:50484] AH00992: ajp_read_header: ajp_ilink_receive failed, referer: https://mydom.com/office/VAADIN/themes/reindeermods/styles.css
[Fri Aug 16 22:08:18.228776 2019] [proxy_ajp:error] [pid 3629:tid 140277591308032] (120006)APR does not understand this error code: [client 192.168.34.1:50484] AH00893: dialog to [::1]:8009 (app.ti-mm.com) failed, referer: https://mydom.com/office/VAADIN/themes/reindeermods/styles.css

And the application show a message that it cannot load javascript resource (js.nocache Vaadin artefact).