If you have issues with loosing the Ethernet connection, loosing the external SD-Card etc. There is a very high chance that your power supply is bad. I had this issue with the wrong power supply (1.5A). So the system boots up, is doing the work, but at some point you drive into very strange issues. If you have this problems also, check the power supply. This will save your time. You need minimum 3A.
On my side the problem is still not solved, but I guess it's still the power supply. I exchanged it with a power supply with 12V/5A DC.
I will offer my insight on power supply topic in a generic way, not directly on UDOO x86. Few times when I purchased x86 based mini PC and the like, I found the PC itself is good, while the power supply units were sourced from the third party (probably by supply chain management per bidding process) and some of them are marginal/bad. Key finding is that cheap one, or power supply unit designed for other purposes (e.g., LED lighting) cheap out by using thinner DC cord, minimal (or no) DC output filter capacitor. The symptom is when x86 based board does its CPU-bursting thing, power demand peaking instantaneously while P.S. cannot handle it thus voltage drop. Even briefly, such case will cause brownout condition and CPU will be halted. This has no direct relationship with P.S. rating (3A or 5A) but quality of the goods. I typically add one additional 2200uF filter capacitor on questionable P.S. unit and the problem goes away.
