Cost basis and ATH portfolio value changes over time?

I am using BTC as my base currency.

I make a single transaction for a coin/token (LINK/BTC or similar pair) and I know exactly what the order closed at. The cost basis is not showing what the order price was (or anywhere close to reflect fees etc).

On top of that. It changes over time. I can check it one day and the cost basis shows one number in BTC cost basis, and the next day it will show something different even though there has been no new transactions.

Similar, my all time highs on my portfolio measured in BTC fluctuate over time. The all time high is the all time high and shouldn’t change. IE, today, my all time high is 1.05BTC (image included). I ll update tomorrow or the next to show the difference.

image

And here is the current cost basis.


Here is the cost basis several days later. Everything has changed.

image
And here is the ATH, also on May 11th but the value has changed from 1.05BTC to 0.98 BTC… this is HISTORICAL data… how is it changing over time?