One of my players noticed that the second sentence of the spell description is missing.

While perceiving through the beast's senses, you gain the benefits of any special senses possessed by that creature, though you are blinded and deafened to your own surroundings.

Did the D&D Beyond team use some sort of OCR software to fill out their data? Interestingly enough, the Beast Sense spell is only one of three instances in the spell section of the PHB where a page starts with a full sentence mid-paragraph (meaning that the previous page ended with a complete sentence) and of those three instances it's the only one where the previous page had an image column empty of text. I'm wondering if maybe the pattern recognition algorithm simply goofed in handling that.

There are only a small handful of these "image columns," and for the rest of them there are obvious cues that pattern recognition algorithms would pick up on.

Or maybe this was all just manually entered and someone messed up. :) Although I'd be surprised if they would have spent resources on manual data entry...

Can confirm, that sentence is in the DDB compendium of the Player's Handbook, but missing from the DDB spell description for Beast Sense.

The removal of that line does not appear in the most recent WotC erratum for the PHB (12th printing) as either new nor from a previous version:

https://media.wizards.com/2018/dnd/downloads/PH-Errata.pdf