Thanks for that - the suggested solutions in the linked thread resolved the issue.
For anyone experiencing the exact same issue [ centos 7, FTL successfully updated to 5.13, Pi-hole version is v5.7 (Latest: v5.8.1), AdminLTE version is v5.9 (Latest: v5.10.1) ], the following works:
cd /var/www/html/admin
git status
git remote -v
git fetch
git status
git remote -v
-> Running pihole -up now will allow proper update of AdminLTE to latest version.
-> Next
cd /etc/.pihole/
git status
git remote -v
git fetch
git status
git fetch
git status
git remote -v
-> Running pihole -up now will allow proper update of pihole CORE to latest version.
Solution worked for all 5 Centos 7 machines, both ARM and Intel.