No need to apologize! 
I just searched for ‘TTA’ and the first thing in the list was the announcement of this change: Change to how TTA() works . Does that answer your question? (Many of the other search results cover the same issue - so have a look at them too if you have a chance.)
Having said that, it looks like @eduardopoleo has given you a good solution there. (If you find a notebook where this fix hasn’t been applied, please either let me know so I can fix, or provide a PR, so students in the future don’t have to deal with this.)