Did you read this thread? After you upgraded to Merlin, did you complete all the install instructions (e.g. factory reset, re-configure, etc.)?
When I purchased my 88u's here in China I played around with it for a while and changed China to United States using the original FW shipped with the routers. I don't even remember what version that was. All my wireless devices worked fine with China or the U.S. setting (keeping in mind that some of the available frequencies were different, as I recall). I didn't see any appreciable performance differences so I changed it back to China. Along the line I updated to the latest (at the time) factory FW, then to Merlin's 380.57 and now to 380.58 (thanks Merlin). I'm perfectly happy with my wi-fi performance. Out of curiosity, why do you want to change territory?
Yes I did. I'm not sure whats happening because I just turned on the wifi on my android phone again and the router crashed again. (with China region set). I expect I've done something wrong. I would prefer to stick with Merlin firmware as it has done me well on my AC66 router.
I've got some stuff to do now, but I will have another furtle with it tomorrow.