Thanks all for checking this out.
As I noted in my edit to the original post, I misspoke, this occurs on sign-up, not sign-in.
Here are some screen shots. It occurs on both Firefox and Chrome on our Discourse site, but interestingly not on the sign-up here, on Meta - it’s close, but the page aligns slightly down. Our site, if you’d like to test, is discuss.uplift.us. We’ve kept up to date with all the Discourse updates, and haven’t applied any custom styling yet.
I’ve found that the moto e5 generally displays sites the same as an iPhone 5; I don’t have one handy to test, but I wonder if the same might occur on an iPhone 5.
Our site (This is Chrome, but it’s identical on Firefox):
