What are the potential causes of my fingers going numb when riding?
I'd suggest a change of gloves, but it seems that you already did so. If you haven't already, give a try to padded gloves.

You could try to check your grips and upgrade to ergonomic ones or changing the handlebar tape. Adjusting the saddle height might be a good idea too.

If the issue persists, perhaps the size of the handlebars or bike aren't adequate for your build, in which case you probably would benefit from getting a bike that fits you. See this question for additional suggestions.

As a last resort, and if you try all the possible adjustments, have a fitted bike, and still the numbness persists, I'd suggest you go to your doctor and discuss the issue.