WordPress Debug: WP_Http & Notice | briarnblaar.co.za | Critical Error Screen

Question

I have a Pipe Smokers forum briarnblaar.co.za - which I created on WordPress using the disputo theme and bbPress forum.

My site frequently gives a white screen with a critical error message and then I need to reload the screen. I installed the Debug bar, enabled WP_DEBUG and when I go to my page, I see a white banner with the following message:

Notice: Trying to get property 'ID' of non-object in /home/briardsj/public_html/wp-includes/class-wp-query.php on line 4027

Notice: Trying to get property 'post_title' of non-object in /home/briardsj/public_html/wp-includes/class-wp-query.php on line 4029

Notice: Trying to get property 'post_name' of non-object in /home/briardsj/public_html/wp-includes/class-wp-query.php on line 4031

Notice: Trying to get property 'post_type' of non-object in /home/briardsj/public_html/wp-includes/class-wp-query.php on line 4179"

When I click on the debug button, I get

A warning:

NOTICE: wp-content/plugins/disputo-features/so-widgets/disputo-forums/tpl/disputo-forums-template.php:21 - Undefined variable: disputo_thumbnail require('wp-blog-header.php'), require_once('wp-includes/template-loader.php'), include('/themes/disputo/page_template_2.php'), the_content, apply_filters('the_content'), WP_Hook->apply_filters, SiteOrigin_Panels->generate_post_content, SiteOrigin_Panels_Renderer->render, SiteOrigin_Panels_Renderer->render_row, SiteOrigin_Panels_Renderer->render_cell, SiteOrigin_Panels_Renderer->render_widget, SiteOrigin_Panels_Renderer->the_widget, SiteOrigin_Widget->widget, include('/plugins/disputo-features/so-widgets/disputo-forums/tpl/disputo-forums-template.php')

I also get a message under the WP_Http tab:

[class] => Requests
[stack_trace] => Array
        (
            [0] => Debug_Bar_WP_Http->after_http_request
            [1] => WP_Hook->apply_filters
            [2] => WP_Hook->do_action
            [3] => do_action('http_api_debug')
            [4] => WP_Http->request
            [5] => WP_Http->post
            [6] => wp_remote_post
            [7] => spawn_cron
            [8] => wp_cron
            [9] => WP_Hook->apply_filters
            [10] => WP_Hook->do_action
            [11] => do_action('init')
            [12] => require_once('wp-settings.php')
            [13] => require_once('wp-config.php')
            [14] => require_once('wp-load.php')
            [15] => require_once('wp-admin/admin.php')

I have no coding knowledge nor experience. Can someone please in laymen's terms tell me what should I do to get this sorted?

I would really appreciate any help. Thank you in advance.