Ipad Gmail links no longer open
I had the same problem.  One suggestion on the web was deleting the gmail app from my iPad and downloading it again.  I tried that, but I couldn't download the app again because it said the new version of gmail didn't work on my old iPad.
So now we know why the links weren't working.

So then I went into Google on my iPad and opened my gmail account from there.  It's not as convenient as using the app, but at least the links work fine.