Workflows created with a custom Task or a regular Task, while they send the notification via email, they are not adding a new task to the Sharepoint task list. This is happening in different sites in the entire web application. Also, the link to the task (sent via email) has the following message: "Sharepoint Task Page not available." not sure if this is related to the tasks not being created though.
I hope you are well. Within the workflow are you using any sharepoint integration elements?, if so are you able to test out the sharepoint site collection URL here to see if this works ? This should be within the Sharepoint integration wizard.