Lowered CR after upgrading gems (Ruby, Sapphire, etc.)

OK so i upgraded sapphire gem to lvl 6 and my cr dropped? I was at Challenge rift lvl 285 and got to 39200 cr checking my characters stats. Now I’m at 38745 cr and can barely make through challenge rift lvl 272. Any help or advice? Thanks

Non-legendary gems, such as Sapphires, have no impact on your Combat Rating so, if you’ve gone from 39200 to 38745 CR, a loss of 455 CR, it’s not because of that.

Did you leave a Warband, and haven’t joined another one? Leaving a WB causes you to immediately lose the CR bonus you’d get from the Tableau level.

Did you get a new equipment item and you didn’t transfer the rank of the replaced item to the newly equipped one?

Did you swap out a legendary gem?