After much troubleshooting I finally figured out which mirror has a stale repomd.xml file that was resulting in random emails from yum-cron-hourly reporting

"/etc/cron.hourly/0yum-hourly.cron:

Not using downloaded updates/repomd.xml because it is older than what we have:
Current : Fri Apr 15 10:38:44 2022
Downloaded: Thu Mar 10 15:20:01 2022"

I went through the Mirrorlist on one of my CentOS 7 installs and manually updated the repo file to try each mirror and did a yum check-update. Finally found that http://mirror.dal.nexril.net/centos/7.9.2009/updates/x86_64/ was the mirror causing the issue. See below for excerpt from CentOS-Base.repo file and then yum check-update run at command line. Other mirrors in my mirrorlist.txt file reported no such issue.

"#released updates
[updates]
name=CentOS-$releasever - Updates
#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=updates&infra=$infra
baseurl=http://mirror.dal.nexril.net/centos/7.9.2009/updates/x86_64/"

"# yum check-update
Loaded plugins: fastestmirror, priorities
Loading mirror speeds from cached hostfile
* base: mirror.dal.nexril.net
* extras: mirror.steadfastnet.com
base | 3.6 kB 00:00:00
extras | 2.9 kB 00:00:00
updates | 2.9 kB 00:00:00
Not using downloaded updates/repomd.xml because it is older than what we have:
Current : Fri Apr 15 10:38:44 2022
Downloaded: Thu Mar 10 15:20:01 2022"