Google reporting 503s on pages that return no results for filters

Google reported a bunch of 503s when crawling a site that I built with Kirby. When checking into this, every 503 as far as I could tell was a page with a filter string that returned no results, like this one:

I do not know if there was an actual issue with the site when Google was crawling it that would have caused this, or if there’s something about this page that would throw a 503. Does anybody know how I can figure this out to make sure there’s no actual 503 happening here somewhere? I mean, my browser doesn’t report a 503, but maybe if there’s an individual resource that’s doing that it could cause an issue.