I have several Note 3s, and they all get like this. I think the problem is the antenna connector between the circuit board and the antenna that’s built into the rear cover. If I clean the contact, it works better for a while. I thought I had fixed it by putting conductive grease on the contact, but after really great results, it only lasted a week. I just tried prying the motherboard contact spring up a little bit, and I’m now getting a good GPS lock again. Darn that contact is right in the corner of the phone, where chassis flexing can easily mess with it! You only need to take the back cover off to get to the contact, and those instructions are here: 三星 盖乐世 Note 3 后壳更换 On the N900 US variants of the phone, the location of the GPS contact is in the upper right when looking from the front of the phone (or the inside of the removed back case). Antenna locations for N900 variants can be found here: Antenna locations for international (9005) models seems a little different.