Here is an extract from the php-fpm error log, from a single page load.
Nothing in the apache error log.
[05-Mar-2018 09:24:25 Europe/Rome] [2018-03-05 09:24:25] EXCEPTION: (Exception) Trying to read configuration "security.alternate-file-domain" before configuration has been initialized. at [<phabricator>/src/infrastructure/env/PhabricatorEnv.php:334]
[05-Mar-2018 09:24:25 Europe/Rome] arcanist(head=stable, ref.master=dcd7ef66d0e4, ref.stable=8fe1d7701e5d), phabricator(head=stable, ref.master=584495215301, ref.stable=ae7236c7a413), phutil(head=stable, ref.master=dedf260c7755, ref.stable=74e27a2b4a47)
[05-Mar-2018 09:24:25 Europe/Rome] #0 <#2> PhabricatorEnv::getEnvConfig(string) called at [<phabricator>/src/aphront/response/AphrontResponse.php:108]
[05-Mar-2018 09:24:25 Europe/Rome] #1 <#2> AphrontResponse::newContentSecurityPolicyHeader() called at [<phabricator>/src/aphront/response/AphrontResponse.php:91]
[05-Mar-2018 09:24:25 Europe/Rome] #2 <#2> AphrontResponse::getHeaders() called at [<phabricator>/src/aphront/response/AphrontHTMLResponse.php:9]
[05-Mar-2018 09:24:25 Europe/Rome] #3 <#2> AphrontHTMLResponse::getHeaders() called at [<phabricator>/src/aphront/sink/AphrontHTTPSink.php:107]
[05-Mar-2018 09:24:25 Europe/Rome] #4 <#2> AphrontHTTPSink::writeResponse(PhabricatorConfigResponse) called at [<phabricator>/src/aphront/configuration/AphrontApplicationConfiguration.php:302]
[05-Mar-2018 09:24:25 Europe/Rome] #5 <#2> AphrontApplicationConfiguration::writeResponse(AphrontPHPHTTPSink, PhabricatorConfigResponse) called at [<phabricator>/src/aphront/configuration/AphrontApplicationConfiguration.php:81]
[05-Mar-2018 09:24:25 Europe/Rome] #6 <#2> AphrontApplicationConfiguration::runHTTPRequest(AphrontPHPHTTPSink) called at [<phabricator>/webroot/index.php:17]
[05-Mar-2018 09:24:25 Europe/Rome] #7 phlog(Exception) called at [<phabricator>/src/aphront/response/AphrontUnhandledExceptionResponse.php:20]
[05-Mar-2018 09:24:25 Europe/Rome] #8 AphrontUnhandledExceptionResponse::setException(Exception) called at [<phabricator>/webroot/index.php:21]
[05-Mar-2018 09:24:25 Europe/Rome] [Core Exception/Exception] Trying to read configuration "security.alternate-file-domain" before configuration has been initialized.
#0 /home/repo/phabricator/src/aphront/response/AphrontResponse.php(108): PhabricatorEnv::getEnvConfig('security.altern...')
#1 /home/repo/phabricator/src/aphront/response/AphrontResponse.php(91): AphrontResponse->newContentSecurityPolicyHeader()
#2 /home/repo/phabricator/src/aphront/response/AphrontHTMLResponse.php(9): AphrontResponse->getHeaders()
#3 /home/repo/phabricator/src/aphront/sink/AphrontHTTPSink.php(107): AphrontHTMLResponse->getHeaders()
#4 /home/repo/phabricator/src/aphront/configuration/AphrontApplicationConfiguration.php(302): AphrontHTTPSink->writeResponse(Object(PhabricatorConfigResponse))
#5 /home/repo/phabricator/src/aphront/configuration/AphrontApplicationConfiguration.php(81): AphrontApplicationConfiguration::writeResponse(Object(AphrontPHPHTTPSink), Object(PhabricatorConfigResponse))
#6 /home/repo/phabricator/webroot/index.php(17): AphrontApplicationConfiguration::runHTTPRequest(Object(AphrontPHPHTTPSink))
#7 {main}
[05-Mar-2018 09:24:25 Europe/Rome] [2018-03-05 09:24:25] EXCEPTION: (Exception) Trying to read configuration "security.alternate-file-domain" before configuration has been initialized. at [<phabricator>/src/infrastructure/env/PhabricatorEnv.php:334]
[05-Mar-2018 09:24:25 Europe/Rome] arcanist(head=stable, ref.master=dcd7ef66d0e4, ref.stable=8fe1d7701e5d), phabricator(head=stable, ref.master=584495215301, ref.stable=ae7236c7a413), phutil(head=stable, ref.master=dedf260c7755, ref.stable=74e27a2b4a47)
[05-Mar-2018 09:24:25 Europe/Rome] #0 <#2> PhabricatorEnv::getEnvConfig(string) called at [<phabricator>/src/aphront/response/AphrontResponse.php:108]
[05-Mar-2018 09:24:25 Europe/Rome] #1 <#2> AphrontResponse::newContentSecurityPolicyHeader() called at [<phabricator>/src/aphront/response/AphrontResponse.php:91]
[05-Mar-2018 09:24:25 Europe/Rome] #2 <#2> AphrontResponse::getHeaders() called at [<phabricator>/src/aphront/response/AphrontHTMLResponse.php:9]
[05-Mar-2018 09:24:25 Europe/Rome] #3 <#2> AphrontHTMLResponse::getHeaders() called at [<phabricator>/src/aphront/sink/AphrontHTTPSink.php:107]
[05-Mar-2018 09:24:25 Europe/Rome] #4 <#2> AphrontHTTPSink::writeResponse(PhabricatorConfigResponse) called at [<phabricator>/src/aphront/configuration/AphrontApplicationConfiguration.php:302]
[05-Mar-2018 09:24:25 Europe/Rome] #5 <#2> AphrontApplicationConfiguration::writeResponse(AphrontPHPHTTPSink, PhabricatorConfigResponse) called at [<phabricator>/src/aphront/configuration/AphrontApplicationConfiguration.php:81]
[05-Mar-2018 09:24:25 Europe/Rome] #6 <#2> AphrontApplicationConfiguration::runHTTPRequest(AphrontPHPHTTPSink) called at [<phabricator>/webroot/index.php:17]
[05-Mar-2018 09:24:25 Europe/Rome] #7 phlog(Exception) called at [<phabricator>/src/aphront/response/AphrontUnhandledExceptionResponse.php:20]
[05-Mar-2018 09:24:25 Europe/Rome] #8 AphrontUnhandledExceptionResponse::setException(Exception) called at [<phabricator>/webroot/index.php:21]
[05-Mar-2018 09:24:25 Europe/Rome] [Core Exception/Exception] Trying to read configuration "security.alternate-file-domain" before configuration has been initialized.
#0 /home/repo/phabricator/src/aphront/response/AphrontResponse.php(108): PhabricatorEnv::getEnvConfig('security.altern...')
#1 /home/repo/phabricator/src/aphront/response/AphrontResponse.php(91): AphrontResponse->newContentSecurityPolicyHeader()
#2 /home/repo/phabricator/src/aphront/response/AphrontHTMLResponse.php(9): AphrontResponse->getHeaders()
#3 /home/repo/phabricator/src/aphront/sink/AphrontHTTPSink.php(107): AphrontHTMLResponse->getHeaders()
#4 /home/repo/phabricator/src/aphront/configuration/AphrontApplicationConfiguration.php(302): AphrontHTTPSink->writeResponse(Object(PhabricatorConfigResponse))
#5 /home/repo/phabricator/src/aphront/configuration/AphrontApplicationConfiguration.php(81): AphrontApplicationConfiguration::writeResponse(Object(AphrontPHPHTTPSink), Object(PhabricatorConfigResponse))
#6 /home/repo/phabricator/webroot/index.php(17): AphrontApplicationConfiguration::runHTTPRequest(Object(AphrontPHPHTTPSink))
#7 {main}