https://en.wikipedia.org/w/api.php?action=query&formatversion=2&list=globalblocks&bgip=20.95.0.0/18
This makes a query about 20.95.0.0/18 but returns the following:
{ "error": { "code": "cidrtoobroad", "info": "IPv6 CIDR ranges broader than /19 are not accepted.", "docref": "See https://en.wikipedia.org/w/api.php for API usage. Subscribe to the mediawiki-api-announce mailing list at <https://lists.wikimedia.org/postorius/lists/mediawiki-api-announce.lists.wikimedia.org/> for notice of API deprecations and breaking changes." }, "servedby": "mw-api-ext.codfw.main-7c648c5d98-qtcxx" }
That is, the API misrecognizes the IPv4 CIDR as an IPv6 CIDR and thinks that the CIDR limit is /19 rather than /16.