This issue sounds unrelated to PHP though. Or maybe not!
In apache2.conf you do have a log directive, right?
You can add: “LogLevel info” in there, so ‘systemctl restart apache2’, try accessing the site and check the error log for any clues.
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Best regards,
Odhiambo WASHINGTON,
Nairobi,KE
+254 7 3200 0004/+254 7 2274 3223
In an Internet failure case, the #1 suspect is a constant: DNS.
“Oh, the cruft.”, egrep -v ‘^$|^.*#’ ¯_(ツ)_/¯ 
[How to ask smart questions: http://www.catb.org/~esr/faqs/smart-questions.html]