Sometimes that can happen after a major update, you can try clearing the cache partition and that usually helps.
You might also want to give it a couple of days and if it does not improve I would recommend a factory reset.
Thanks for posting this. I too did the Nougat upgrade on the Nova Plus and would harshly advise against it. The phone is much slower running this OS, especially the camera app which is very frustrating when you are trying to capture the moment. Google Drive doesn't not crash every time I load like it did on Marshmalllow which is a plus because I use it daily. That is the ony plus of upgrading to Nougat.