As ketones are used or produced they go up and down. It’s not easy to say whether those are normal variances because, for you, they could be. And, in a few months, they could be totally different under the same circumstances.
As insulin goes up (usually prompted by blood sugar rising or a meal), ketone production slows or stops. Some ketones could be used or dumped from your previous reading, leading to the lower reading. So, in response to the question in your title, yes, blood ketone reading variances are normal with eating or throughout the day. This is why many people say it’s not worth chasing numbers.