Error when Menu Access plugin is enabled

In our development website we have installed PayPlans in order to restrict access to some menu element.

However, when we enable the plugin we get a blank page with the following error message: "Error displaying the error page".

Enabling the Joomla debug and setting the Error Reporting to "Development", the error does not says too much more: "Error displaying the error page: Call to a member function getActive() on null: Call to a member function getItems() on null"

The error_log file does not register any information about this issue.

We're running Joomla 3.8.2 on PHP 7.1.12.

In addition to PayPlans 3.6 Build :3 we have installed:
* HelloMaps v1.5
* Akeeba Backup Core 5.6.0
* K2 v2.8.0
* Simple Image Gallery Pro v3.1.0
* JA Hotel 1.0.5 template

We have applied the patch provided at https://stackideas.com/forums/menu-access-plugin-making-joomla-menu-dissappear but the error still appears, so we went back to the original file.

Any advice on how to solve this or at least on how to get more detailed information on the error origin?

Regards,