We know that Beau suddenly and inexplicably changed his destination from his apartment in Brentwood to the address in Santa Monica. We don't know if he was actually going to that address, or was using it as a convenient drop-off point to go somewhere else. We also know that Beau's phone called 911 using the Uber app, but we can't be sure it was deliberate. Additionally, we know his phone was turned off soon afterwards, preventing contact by 911 and also any further tracking of his location. That was presumably deliberate, though we can't be sure who did it.
All together, those things suggest something was happening to Beau that was quite sudden and unexpected.
I apologize if this is known and I've somehow missed it, but do we know if the destination was changed before or after the 911 call? The order of those two things might be important.
If Beau was OD'ing or something of that nature, my thinking is that he might have initially called 911 before changing his mind and asking to be taken somewhere he thought he could get help. If he knew of a drug den near the Berkeley Street address, he might have thought he could get Narcan there, for example.
The only puzzling thing about that theory would be the Uber driver. If you've got someone OD'ing in your car, I presume you're going to notice and remember.