MyBB 1.8.19 not working with PHP 7.3

[simoncn]

My hosting provider is dropping support for PHP 5.6 and will shortly move all hosted applications to PHP 7.3. This is causing issues with my hosted forum. When I go to the Admin CP Plugins page, there is a 503 error and I cannot view my installed plugins. It works correctly with PHP 5.6. I am on 1.8.19 which is the latest version supported by my hosting provider. Any help or pointers would be much appreciated. Many thanks.

[Crazycat]

First, disable all plugins in ACP > Configuration > Settings > General Configuration. Your forum will work fine. Then, reactivate plugins one by one to check which is causing this trouble.
If you can't access to the plugin page when they are all disabled, do this:
- save all the content of inc/plugins/ in a safe place (your computer is ok)
- delete the content of inc/plugins/ in your forum
- go to plugin page (it may work now)
- upload the saved files one by one, and refresh the plugin page each time. When a 503 error occures, you find the faulty plugin.