You might see the following error if Enable Content Sniffing protection is selected under the Content Sniffing protection section in Salesforce Setup: Refused to execute script from 'https://www.abc.com/resource/1225399...enametoinclude' because its MIME type ('text/plain') is not executable, and strict MIME type checking is enabled.
When a user creates an ActionGrid custom action, a custom MIME type is automatically associated with it which is not supported in Salesforce security because the MIME type is not standard.
If a custom action is not showing under the actions menu even when it has been enabled in ActionGrid Setup, review your developer console:
Chrome - Chrome Menu -> More Tools -> Developer Tools -> Console or hit the F12 key
FireFox - FireFox Menu -> Developer -> Browser Console or hit Ctrl + Shift + k
Edge and IE - Edge/IE Menu -> F12 Developer Tools or hit the F12 key
To fix the issue, go into Salesforce and select Setup -> Security Controls -> Session Settings and then uncheck the Enable Content Sniffing protection checkbox under the Content Sniffing protection section.