Cache max-age and CRLDP
Apparently if your CRLDP end point doesn't set max-age in the response header browsers may use a heuristic method to guesstimate how long to cache it, like (current date - last modified date) / 10. What this means practically is that if say your root CA CRL is refreshed once a year, if a client happens to download it at the wrong time, the browser will consider the cached file to be fresh even if current date is past the NextUpdate date set on the CRL (and remember Chromium browsers don't use CAPI2 to handle CRLs anymore).
So basically in addition to the intended RFC5280 mechanisms for determining when to refresh the cached CRL, it's also subject to browser-side rules on how long to cache files, since CRLs are handled like any other downloaded content under Chromium.