It may not be only iOS. Days ago I created a tag on my Mac. When I search by the tag I, the result shows there are 2 notes to which it applies, but then on my Mac and Android phone, I can not open the notes.
I just sorted this out with Evernote Support.
1) Quit Evernote
2) Open Finder
3) From the menu Go / Go to Folder
4) paste in ~/Library/Containers
5) Delete the folder called Evernote
6 Go to evernote.com/download and reinstall the app.