There is a definite scoring bug for this lesson (B2 El Futuro Perfecto).
I, as well as others, have reported similar bugs for other lessons as well.
Please review my most recent approximately 30 test scores. Since this is the last lesson in B2 that has not reached 100% I put it as the only lesson in a notebook to facilitate rapid testing to ultimately achieve 100%. As you can see from my test results where I had no errors whatsoever, the scores bounce up and down from as high as the 90s to the 50s percent, again with no test errors.
The time is overdue to fix this bug, which has been around for a long while!!!
Meanwhile of course I'll move on to C1...