I had an issue with one of the 7.x upgrades too. There was a weird efibootmgr upgrade as part of.. 7.3 i think it was? Maybe 7.2?

Anyway, here is a thread that I just found that seems to summarize the pain I went through at the time (alas, my path was far more circuitous)...

https://lists.centos.org/pipermail/centos/2018-January/16786...