Just got it again while doing revision but with a different translation. So do these Zombie sentences only appear on the app? Not on the website?
It appears worse on the apps, since they only seem to be updated occasionally.
It's a system wide problem with Duolingo but less obvious on the professionally produced courses and to be honest on many other crowdsourced ones as well.
We had a particular problem in that one of our, now departed, contributors made a large number of mistakes that we didn't spot until after the course was released to beta. So we have had more corrections to make than many other courses.
The process of deleting erroneous sentences seems very hit and miss but now that we've started working on the revised course it will be possible to address this problem.
In reference to this sentence, there are about 200 sentences with gyda in them so it'll be hard to locate and sort it out, but maybe it'll be possible.