Q: USB Ethernet Adapters Useless

El Capitan broke many drivers or more accurately old drivers were not compatible with El Capitan. Are you saying that rather than say going from 10.10.5 to 10.11.x broke your drivers that 10.11.3 to 10.11.4 broke your USB Ethernet driver?

Regardless, most of the USB Ethernet adapters for Mac I have seen use the same Asix chipset and hence can use the same driver. See http://www.asix.com.tw/products.php?op=pItemdetail&PItemID=131;71;112

They don't seem to have updated it since February so if your issue is purely a 10.11.4 one then you may have to wait a bit, if it is because you have only recently switched to El Capitan then as you can see they do list support for El Capitan at least as of February.

Yes, I was using a 3rd party USB adapter and I just went and bought a thunderbolt ethernet adapter on the advice of Apple and that doesn't work either.

A Thunderbolt Ethernet adaptor does not use USB. There is another issue at hand involving that adapter.

True, thunderbolt uses thunderbolt. But if I assume that if USB and thunderbolt adapters are both not working after the update then the issue is with the ethernet connection generally.

Hi @chrislogan - I don't know if you're still having this issue but an update from me - I went to the apple store and they confirmed no hardward issues but no internet through USB or thunderbolt (or in fact Wi-Fi). Because the ethernet was still recognised they were able to boot from a triage drive on their own network and confirm that Wi-Fi and ethernet both worked. The advice I was given was that I needed to start again and re-install El Capitan. However, I restarted in the store and whatever they did somewhow triggered something and it now sort of works - but they don't know why. I can't plug it in when the machine is on, I have to restart it every time, but for now that will do over finding the time to format the drive. Basically time machine backup and a reinstall is the solution - but it's not ideal.

@mrtropicana and @chrislogan, I am having the same issue; however, last week before I updated to 10.11.4 (i was previously at 10.11.3) I had to constantly restart my macbook pro (instead of just un-sleep it) to get the thunderbolt to ethernet adapter to work.  Yesterday when I updated to the 10.11.4 it stopped working entirely.  I even tried another thunderbolt ethernet adapter and it didn't work.  Even to test the ethernet cable and adapters I had a friend test their macbook pro (which is 10.11.4) and both adapters worked fine.

I am wondering if it is how my update was installed or if something went wrong with my update.  So to try and fix the issue i have removed all of the network options and restarted several times to no avail.  Also now that I have removed the Thunderbolt Ethernet adapter from my network settings I can't seem to add it back via the + symbol.  When I click that I don't get an option in the Interface dropdown for Thunderbolt Ethernet.

I guess I could try to reset the NVRAM / PRAM and SMC but neither of the Apple help pages for those settings make me think they will fix this issue.  If you find a resolution please let me know because it is very frustrating.  Also I hope I can figure out why it required me to restart every time to recognize the Thunderbolt Ethernet adapter before the update.