Bought two UMI X2 MT6589T. Initially both worked fine. After 10 days one phone started losing network signal (both phones work under same carrier). Now it works erratically. Tried new ROMS, always the same problem; opened the phone, examined antennas' sittings (everything fine) re-tightened all screws but signal gets lost very often, in locations where second phone shows four to five bars. I also swapped SIMS, still bad phone stays bad phone. Any idea please?
If the phones are on the same firmware and you're still having a problem, it's likely an antenna or other hardware issue. I'm stating the obvious... What you already know.
It's interesting it worked fine at first. Possibly a faulty 'line' on the motherboard. It's just a wild guess. Do you still have time to return to the seller?
I think that's bug from MT6589 or MT6589T firmware, you can fix it with format the phone totally then install the new firmware if available, otherwise, even fix it, but that would be happen again. My P7 (probably MT6577) also like that, but I did customize the ROM and combined system then fix it and so far so good till now.