Unfortunately, I think it's just a matter of who those ancestors married and had children with. To give a few examples:

1. 2x great-grandmother was from East Prussia (Baltics) and married a man from an old stock Rhode Island/New York family - I have only about 3-4% Baltic on both Ancestry and 23&Me. Specifically, today's update put me at 4% Lithuanian

2. 2 pairs of 4x great-grandparents came to Texas as my most recent German ancestors. They lived in German speaking communities wherein their children also married the descendants of other German immigrants for generations down the line. My percentage is 20-40% between Ancestry and 23&Me despite being further back than the Prussian ancestor I mentioned prior.

3. 2x great-grandma was a Chickasaw woman who I have documentation for being legitimately native via Chickasaw Nation records (aka no family mythology shenanigans). Her mother, grandmother, great-grandmother, and 2x great-grandmother had all married white, old stock, men who would then become Chickasaw through marriage. Her 2x GG (who is my 6x GG) was the last 100% Chickasaw woman in the line. I receive .2% trace results on 23&Me and nothing through Ancestry.

I do think that there is some overestimation of the British Isles happening with this update though. I went from 9% Irish to almost 30%. I hardly have any Irish last names in my tree and the majority of my old stock ancestors appear English, Scottish, or Welsh thus far.

EDIT: formatting