The Spanish audio incorrectly pronounces “sea” as the English word “sea.”
Do you mean a) the audio that sounds when you click on a specific word or b) the Read Aloud audio that reads the whole text when you click the play button at the bottom of a page of text?
If the answer is (b), note that this audio is generated by your specific browser and device, and if multiple voices are available on your device you can switch them here: Introducing Read-Aloud - Readlang Blog
For me, the voice (a) that sounds when clicking a specific word is pronouncing it the Spanish way.
I experienced this as well for scenario a, but only very seldomly and only for Spanish words that are identical or very similar to English words. I can’t remember the exact words though 
This happens occasionally with Microsoft voices on Edge when the word is spelt the same way as as English word. I even heard it happen on a YouTube language story-telling video the other day, which was a sure give-away that TTS voices were being used.
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