from what i can tell its a secret as no replies about it, but you can get around it by clicking the previous completed ring then back to the ring your on should stop the graying out but not exactly ideal

this was resolved this morning by the dev team 

No it was not as its still happening!!!!

I agree - still a problem

Hi! Please let me know your Player ID and coordinates. A screenshot reflecting this issue would be also helpful. Thanks a lot!

my apologies, as it was resolved on FB servers I naturally assumed it had been resolved everywhere 

the workaround in the second post should work in the meantime. 

Please let Plarium have your coordinates and player id to help them resolve it