Hello. I tried use json-sync feature and discover few things.
1. Instead of timestamp as variant, ACF can check by getting hash from file content. Developer can be edit file, without keeping in mind, that timestamp must be modified.
2. Looks like for me, if i delete field from json file, and change timestamp, acf not display sync ability. Can be good to have it.
I am using Advanced Custom Fields PRO 5.5.5
