I had the exact same problem with a FireWire 800 2.5" SSD, running off FireWire power (which is much, much more than USB power). It'd work great and then out of the blue, the computer would get the spinning beachball of death and couldn't recover from that. There was no consistency in the pattern. It could be at any time, and in any application. However, between crashes it would run perfectly fine, for many, many hours continuously.
I then plugged in the FW enclosure into AC power and it worked perfectly after that. Ran it for over a year like that with no crashing issues.
In my case it was absolutely clear that despite the fact that FW can provide quite a bit of bus power, the reliability and/or amount of that power still just wasn't good enough to run that drive + enclosure reliably. While the Samsung T3 is built to run off USB power, there is a possibility in your case it just doesn't. USB power is way less and is pretty borderline for a drive. and the stability of the power may also be an issue. I've recommended in the past to people, ideally if you want an SSD boot drive, having an external power supply takes this potential problem out of the equation.
EDIT:
Here we go. Bus power usage on that drive can spike to well above 3 Watts:
https://www.anandtech.com/show/1016...mption-measurement-using-plugables-usbctkey/3
This can be a problem in some situations, since under usual circumstances, USB 2.0 power should only provide 2.5 Watts (5 V x 0.5 Amps). USB 3 power can be 4.5 Watts though (5 V and 0.9 Amps) and your 2013 is USB 3, but still I have to wonder if this could be a problem.
tl;dr:
My bus powered FireWire 800 SSD gave similar results and would crash randomly, but all the crashes disappeared when I added supplemental power.
For the Samsung T3, its power usage can spike to well above 3 watts, which would be a huge problem for USB 2.0 ports. It should work on USB 3.0 ports, but I still wonder if in some cases it might be a problem with specific hardware, especially since USB power may not always be completely stable.