Hi there,
You are not alone with this issue, I have written about this and got tons of feedback from others on other forums. The issue primarily impacts newer songs and Apple is aware of the issue. This was an email followup I received in late December after I called Apple to report on this in late November.
You should still be able to create a Genius playlist for songs released up till around summer 2015. Songs released after that time are not likely to work (at the time I write this).
There is reason to be optimistic that the issue will be fixed, Genius has seen an increased presence in the last 2 iTunes updates and Apple has updated the support page for Genius in January.
My recommendation for now is to update Genius. In iTunes, from the 'File' menu select 'Library' and click 'Update Genius'. iTunes should also be automatically updating Genius once a week.
You can also send in your feedback here: https://www.apple.com/feedback/itunesapp.html
I believe the more people that send in to Apple about this issue, the more they will prioritize fixing it.