It sounds like you could be having a theme or plugin conflict. I would suggest trying to use the Health Check plugin to debug https://ww.wp.xz.cn/plugins/health-check/
The plugin will use a default twenty-something theme and deactivate all plugins (only for the logged in user). Activate all your plugins and see if the customizer loads with the plugins and a default theme. If it does then you know it is a theme issue and you will need to contact the theme developer. If you still have the white screen issue deactivate all plugins and activate theme one by one until you find the one with the problem and contact the developer of that plugin.
Hope this gets you headed in the right direction
