got 500 code in response after update

[vahidss]

Hi there, 
 I am facing an issue after upgrading the WHMCS from 8.0.x to 8.1.3.
after the update, almost all requests got 500 code but the response body is valid (almost).
the requests didn't recognize as error_log and saved at access log like these:
 

[06/Jun/2021:08:17:43 +0230] "GET /portal/admin/supportticketpredefinedreplies.php?action=edit&id=1 HTTP/1.1" 500 0 "https://*/portal/admin/supportticketpredefinedreplies.php?catid=2" "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/89.0.4389.114 Safari/537.36"

[06/Jun/2021:08:20:16 +0230] "GET /portal/clientarea.php?action=services HTTP/1.1" 500 0 "https://*/portal/clientarea.php?action=invoices" "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/91.0.4472.77 Safari/537.36"