Strange PHP warning about array_flip

Hi! First of all, thanks a lot for such useful plugin, much appreciated 🙂

The plugin is generating the following warning:

array_flip(): Can only flip STRING and INTEGER values!

I scanned the plugin files and didn’t find this function being used, but I’m sure it’s My Account Customizer that’s generating it. That’s puzzling…

The warning is putting the plugin Query Monitor on red alert.
https://wordpress.org/plugins/query-monitor/

Also, there are these two notices being dropped:

Notice: Undefined variable: core_fields
Notice: Undefined property: wcmamtx_add_frontend_class::$endpoint_key

I know warnings and notices are not errors, although it’s nice to have things running smooth without those 🙂
What’s concerning is that they are being printed everywhere, which means the plugin is leaking on places where it shouldn’t be running at all.

I just checked and yes, you need to review that… for example, the class wcmamtx_add_frontend_class shouldn’t be running on the backend. If we add this check first thing on the constructor, Query Monitor doesn’t goes red on the backend:
if( is_admin() ) return;