I had the same error and it went away when I updated to 87.1
could not find it on my system either. Can’t remember where I saw it but some said they did away with that error in 87.1 on this forum I believe.
Do you have MQTT sensors? I do, and my config has json_attributes. I changed them to json_attributes_topic and the warning went away. However, I changed back because I haven’t yet worked out the actual impact.