After upgrade/update i see errors: Undefined variable/index

Hello, after upgrading WHMCS 5.2x16 to 6.3.2 i checked /admin/error_log and found following errors:

[13-Jul-2017 12:57:33 Europe/Prague] PHP Notice: Undefined variable: params in /home/myusername/public_html/modules/servers/buycpanel/buycpanel.php on line 0

[13-Jul-2017 12:57:33 Europe/Prague] PHP Warning: Missing argument 1 for buycpanel_create_products_table(), called in /home/myusername/public_html/modules/servers/buycpanel/buycpanel.php on line 0 and defined in /home/myusername/public_html/modules/servers/buycpanel/functions.php on line 0

[13-Jul-2017 12:57:33 Europe/Prague] PHP Warning: Missing argument 3 for select_query(), called in /home/myusername/public_html/modules/servers/buycpanel/functions.php on line 0 and defined in /home/myusername/public_html/includes/dbfunctions.php on line 0

[13-Jul-2017 12:57:33 Europe/Prague] PHP Notice: Undefined variable: where in /home/myusername/public_html/includes/dbfunctions.php on line 2097152

[13-Jul-2017 12:57:51 Europe/Prague] PHP Notice: Undefined variable: success in /home/myusername/public_html/modules/servers/prve/prve.php on line 234

[13-Jul-2017 13:03:15 Europe/Prague] PHP Notice: Undefined index: Template in /home/myusername/public_html/modules/servers/prve/prve.php on line 136

[13-Jul-2017 13:03:15 Europe/Prague] PHP Notice: Undefined index: Password in /home/myusername/public_html/modules/servers/prve/prve.php on line 142

[13-Jul-2017 13:03:16 Europe/Prague] PHP Notice: Undefined index: renewals in /home/myusername/public_html/includes/orderfunctions.php on line 0

[13-Jul-2017 13:04:40 Europe/Prague] PHP Notice: Undefined variable: autorecalcdefault in /home/myusername/public_html/admin/clientsservices.php on line 2097152

[13-Jul-2017 13:05:27 Europe/Prague] PHP Notice: Undefined index: Template in /home/myusername/public_html/modules/servers/prve/prve.php on line 136

[13-Jul-2017 13:05:27 Europe/Prague] PHP Notice: Undefined index: Password in /home/myusername/public_html/modules/servers/prve/prve.php on line 142

[13-Jul-2017 13:05:29 Europe/Prague] PHP Notice: Undefined variable: autorecalcdefault in /home/myusername/public_html/admin/clientsservices.php on line 2097152

[13-Jul-2017 13:05:42 Europe/Prague] PHP Notice: Undefined index: Template in /home/myusername/public_html/modules/servers/prve/prve.php on line 136

[13-Jul-2017 13:05:42 Europe/Prague] PHP Notice: Undefined index: Password in /home/myusername/public_html/modules/servers/prve/prve.php on line 142

[13-Jul-2017 13:05:43 Europe/Prague] PHP Notice: Undefined variable: autorecalcdefault in /home/myusername/public_html/admin/clientsservices.php on line 2097152

It seems like two addons/modules have some issue or can it be related to WHMCS itself? Please can you suggest way to debug the cause?

you'll need to check both modules are compatible with your WHMCS version... as per your previous thread, pvre is v6 compatible (a little vague), and according to Marketplace, buycpanel is v6.3 compatible... though it doesn't mean it actually is, just that the developer has marked it as such.

thank you, it indeed seems to be Addon modules related, because it no longer appear when i deactivate Addon module.

instead this error appears in /admin/error_log:

PHP Notice: Undefined index: description in /home/myusernamehere/public_html/admin/configaddonmods.php on line 0

Any way to debug which Addon module .php file is responsible, on which line? I assume i can add error_reporting(E_ALL); line into all main module files that are called in most circumstances, any more simple way? The error appears rather rarely, not daily, and i see it twice in same second.