Server Crashes again and again

Hi,
I am wordpess developer, My client is asking that his server continues to crash again and again. In the php error log , there some php warning giving in wp-include/functions.php, formidable plugin error, etc. Please suggest, how to fix this error and resolve the SERVER CRASH issue. The SERVER CRASH issue fix, is my main requirement.

=>> error msgs as follows::

[26-Dec-2018 13:27:54 UTC] PHP Warning: fread() expects parameter 1 to be resource, boolean given in /home/ltb91h7ov8gj/public_html/wp-includes/functions.php on line 4894
[26-Dec-2018 13:27:54 UTC] PHP Warning: fclose() expects parameter 1 to be resource, boolean given in /home/ltb91h7ov8gj/public_html/wp-includes/functions.php on line 4897
[26-Dec-2018 13:27:54 UTC] PHP Warning: fopen(/home/ltb91h7ov8gj/public_html/wp-content/plugins/formidable-mailchimp/formidable-mailchimp.php): failed to open stream: No such file or directory in /home/ltb91h7ov8gj/public_html/wp-includes/functions.php on line 4891
[26-Dec-2018 13:27:54 UTC] PHP Warning: fread() expects parameter 1 to be resource, boolean given in /home/ltb91h7ov8gj/public_html/wp-includes/functions.php on line 4894
[26-Dec-2018 13:27:54 UTC] PHP Warning: fclose() expects parameter 1 to be resource, boolean given in /home/ltb91h7ov8gj/public_html/wp-includes/functions.php on line 4897
[26-Dec-2018 13:27:54 UTC] PHP Warning: fopen(/home/ltb91h7ov8gj/public_html/wp-content/plugins/formidable-mailpoet/formidable-mailpoet.php): failed to open stream: No such file or directory in /home/ltb91h7ov8gj/public_html/wp-includes/functions.php on line 4891
[26-Dec-2018 13:27:54 UTC] PHP Warning: fread() expects parameter 1 to be resource, boolean given in /home/ltb91h7ov8gj/public_html/wp-includes/functions.php on line 4894
[26-Dec-2018 13:27:54 UTC] PHP Warning: fclose() expects parameter 1 to be resource, boolean given in /home/ltb91h7ov8gj/public_html/wp-includes/functions.php on line 4897
[26-Dec-2018 13:27:54 UTC] PHP Warning: fopen(/home/ltb91h7ov8gj/public_html/wp-content/plugins/formidable-paypal/formidable-paypal.php): failed to open stream: No such file or directory in /home/ltb91h7ov8gj/public_html/wp-includes/functions.php on line 4891
[26-Dec-2018 13:27:54 UTC] PHP Warning: fread() expects parameter 1 to be resource, boolean given in /home/ltb91h7ov8gj/public_html/wp-includes/functions.php on line 4894
[26-Dec-2018 13:27:54 UTC] PHP Warning: fclose() expects parameter 1 to be resource, boolean given in /home/ltb91h7ov8gj/public_html/wp-includes/functions.php on line 4897
[26-Dec-2018 13:27:54 UTC] PHP Warning: fopen(/home/ltb91h7ov8gj/public_html/wp-content/plugins/formidable-polylang/frm-poly.php): failed to open stream: No such file or directory in /home/ltb91h7ov8gj/public_html/wp-includes/functions.php on line 4891
[26-Dec-2018 13:27:54 UTC] PHP Warning: fread() expects parameter 1 to be resource, boolean given in /home/ltb91h7ov8gj/public_html/wp-includes/functions.php on line 4894
[26-Dec-2018 13:27:54 UTC] PHP Warning: fclose() expects parameter 1 to be resource, boolean given in /home/ltb91h7ov8gj/public_html/wp-includes/functions.php on line 4897
[26-Dec-2018 13:27:54 UTC] PHP Warning: fopen(/home/ltb91h7ov8gj/public_html/wp-content/plugins/formidable-signature/signature.php): failed to open stream: No such file or directory in /home/ltb91h7ov8gj/public_html/wp-includes/functions.php on line 4891
[26-Dec-2018 13:27:54 UTC] PHP Warning: fread() expects parameter 1 to be resource, boolean given in /home/ltb91h7ov8gj/public_html/wp-includes/functions.php on line 4894
[26-Dec-2018 13:27:54 UTC] PHP Warning: fclose() expects parameter 1 to be resource, boolean given in /home/ltb91h7ov8gj/public_html/wp-includes/functions.php on line 4897
[26-Dec-2018 13:27:54 UTC] PHP Warning: fopen(/home/ltb91h7ov8gj/public_html/wp-content/plugins/formidable-twilio/formidable-twilio.php): failed to open stream: No such file or directory in /home/ltb91h7ov8gj/public_html/wp-includes/functions.php on line 4891
[26-Dec-2018 13:27:54 UTC] PHP Warning: fread() expects parameter 1 to be resource, boolean given in /home/ltb91h7ov8gj/public_html/wp-includes/functions.php on line 4894
[26-Dec-2018 13:27:54 UTC] PHP Warning: fclose() expects parameter 1 to be resource, boolean given in /home/ltb91h7ov8gj/public_html/wp-includes/functions.php on line 4897
[26-Dec-2018 13:27:54 UTC] PHP Warning: fopen(/home/ltb91h7ov8gj/public_html/wp-content/plugins/formidable-registration/formidable-registration.php): failed to open stream: No such file or directory in /home/ltb91h7ov8gj/public_html/wp-includes/functions.php on line 4891
[26-Dec-2018 13:27:54 UTC] PHP Warning: fread() expects parameter 1 to be resource, boolean given in /home/ltb91h7ov8gj/public_html/wp-includes/functions.php on line 4894
[26-Dec-2018 13:27:54 UTC] PHP Warning: fclose() expects parameter 1 to be resource, boolean given in /home/ltb91h7ov8gj/public_html/wp-includes/functions.php on line 4897
[26-Dec-2018 13:27:54 UTC] PHP Warning: fopen(/home/ltb91h7ov8gj/public_html/wp-content/plugins/formidable-wpml/formidable-wpml.php): failed to open stream: No such file or directory in /home/ltb91h7ov8gj/public_html/wp-includes/functions.php on line 4891
[26-Dec-2018 13:27:54 UTC] PHP Warning: fread() expects parameter 1 to be resource, boolean given in /home/ltb91h7ov8gj/public_html/wp-includes/functions.php on line 4894
[26-Dec-2018 13:27:54 UTC] PHP Warning: fclose() expects parameter 1 to be resource, boolean given in /home/ltb91h7ov8gj/public_html/wp-includes/functions.php on line 4897
[26-Dec-2018 13:27:54 UTC] PHP Warning: fopen(/home/ltb91h7ov8gj/public_html/wp-content/plugins/formidable-zapier/formidable-zapier.php): failed to open stream: No such file or directory in /home/ltb91h7ov8gj/public_html/wp-includes/functions.php on line 4891
[26-Dec-2018 13:27:54 UTC] PHP Warning: fread() expects parameter 1 to be resource, boolean given in /home/ltb91h7ov8gj/public_html/wp-includes/functions.php on line 4894
[26-Dec-2018 13:27:54 UTC] PHP Warning: fclose() expects parameter 1 to be resource, boolean given in /home/ltb91h7ov8gj/public_html/wp-includes/functions.php on line 4897

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