This is just a quick tip / recommendation.
I have an EX2700 that I flashed via TFTP with the 18.x build linked in the wiki. It would constantly crash, particularly when under heavy network traffic (like downloading a large file). Things would look fine, then the wifi would remain connected, but I couldn't even access luci. I pinged the EX2700 during reproduction of the issue and it would report super heavy latency during the large download and then no response after it crashed.
Reboots after that occurred would sometimes result in luci not loading at all.
I adjusted the MTU from the default 1500 to 1452, and now it's rock solid. Bandwidth speeds dropped only slightly with the change -- totally worth it. I suspect the larger transmission unit might have been eating up the very limited qty of memory available for buffers on this device.
So this is just a tip for anyone with an EX2700 experiencing crashing issues like this: try reducing your MTU.