Author Archive Page results in 404 Error. Sometimes…

When I go to one of my site’s author archive page, I get a 404 error. Sometimes. I use the standard /author/name link

So for instance,

https://www.isgap.org/author/joel/ – author has one post but this link generates a 404 error. Same with author “shalemc” and author “phyllis” – all three authors have one post each.

Here’s where it gets weird. author “richard” shows a proper author archive page and a post – but this author has 2 posts. Why is only one showing up?

And the final cherry on top? When I switch to the default WP “2014” theme, Author Archives works great.

Any and all suggestions are welcome because frankly, I am completely at a loss.