Personally i have not seen an RB750 ethernet lockup.
I have zero deployed yet, but was quite active in testing the Ubiquiti Rocket firmwares to try to find out why the Rocket Ethernet port locked up.
I used 2 RB750s as the Bandwidth server and client.
Passing lotsa Gb, the RB750s did not lock up. The Rocket did.
Atheros give out binaries of the core stuff that they want kept secret. Those parts are definitely the same, although i guess that if you Pay Atheros, then you can get a differnt version.
The Userspace or maybe the Kernel interface bits must be vendor-supplied, so the code is different code.
I was told that the Ubiquiti progrmmers were working on it, so there must be a vendor-supplied part.
UBNT then told me to piss off, and banned me forever from their forum.
Don't forget to give me at least a tenner a month, every month