Recently I have installed my own-made theme on my WordPress and after that a few problems have occurred.
Firstly when I upload a photo or file from my site's admin panel it does not show up under Media tab. and when I try to define a thumbnail for a post I cannot see the photos. Therefore I deactivated my own-made theme and changed it to 2017 WordPress theme. after that when I uploaded images they showed up in my Media tab but again when using one of them as a post thumbnail (after reactivating my theme) they showed up like below:
I've tried several ways to fix this issue such as:
1) Deactivating my whole plugins.
2) Increase PHP Memory Limit by editing the wp-config.php file:
define( 'WP_MEMORY_LIMIT', '256M' );
3) Changing file permissions of my site's uploads folder and etc.
Secondly when I activate my own-made theme some times I see the popular white screen of death.(For example when I define a new category and press the publish key I get redirected to a white empty page) And I don't know what problem my theme has that makes this happen.
What changes must be done to my own-made theme in order to fix the white screen of death and uploads issues?