Tried several times to send a list of tasks to my import email address and the tasks are just not being added to the list. In fact, they are not being adding anywhere.

Did a search in RTM to see if they were added in a different list etc. Not seeing them anywhere.

This is not the first time I am using Import tasks and have successfully imported bunch of tasks before. But recently haven't had any success with tasks import.

Has RTM changed anything recently?

Yes. Have followed the instructions to the T and as I said it worked before, but does not any more.