I am facing several speed issues on my Wordpress website. Seeking to identify the causes, I added the plugin BlackBox Debug that identified 33.1 errors with the theme I use, which is well loaded.
I removed the theme and put a basic theme to see if it persisted and the following log was reported, with 12 errors:
Strict (259) is_a(): Deprecated. Please use the instanceof operator on line 392 in file /home/meusite/public_html/wp-includes/post.php
Strict (11) is_a(): Deprecated. Please use the instanceof operator on line 498 in file /home/meusite/public_html/wp-includes/capabilities.php
Strict (3) is_a(): Deprecated. Please use the instanceof operator on line 75 in file /home/meusite/public_html/wp-includes/functions.wp-scripts.php
Strict (2) is_a(): Deprecated. Please use the instanceof operator on line 105 in file /home/meusite/public_html/wp-includes/functions.wp-styles.php
Strict (6) is_a(): Deprecated. Please use the instanceof operator on line 160 in file /home/meusite/public_html/wp-includes/functions.wp-styles.php
Strict (12) is_a(): Deprecated. Please use the instanceof operator on line 197 in file /home/meusite/public_html/wp-includes/functions.wp-scripts.php
Strict is_a(): Deprecated. Please use the instanceof operator on line 37 in file /home/meusite/public_html/wp-includes/functions.wp-styles.php
Strict is_a(): Deprecated. Please use the instanceof operator on line 115 in file /home/meusite/public_html/wp-includes/functions.wp-scripts.php
Strict is_a(): Deprecated. Please use the instanceof operator on line 812 in file /home/meusite/public_html/wp-includes/script-loader.php
Strict is_a(): Deprecated. Please use the instanceof operator on line 729 in file /home/meusite/public_html/wp-includes/script-loader.php
Strict (101) is_a(): Deprecated. Please use the instanceof operator on line 205 in file /home/meusite/public_html/wp-includes/class-wp-error.php
Notice (3) Trying to get property of non-object on line 597 in file /home/meusite/public_html/wp-includes/nav-menu.php
What do these errors mean? How can I fix them?