it's the official repo:

[root@localhost lib]# yum repolist
Last metadata expiration check: 0:00:14 ago on Wed 13 May 2020 08:38:52 PM CDT.
repo id repo name status
AppStream CentOS-8 - AppStream 5,318
BaseOS CentOS-8 - Base 1,661
cassandra Apache Cassandra 3
*epel Extra Packages for Enterprise Linux 8 - x86_64 5,506
*epel-modular Extra Packages for Enterprise Linux Modular 8 - x86_64 0
extras CentOS-8 - Extras 16
zabbix Zabbix Official Repository - x86_64 18
zabbix-non-supported Zabbix Official Repository non-supported - x86_64 1

I guess Prometheus is pretty popular, but I suspect this is a problem with the prometheus agent and not Cassandra.