Chosen Solution
(Rose Gold is old housing and Silver is new housing) I’ve recently replaced the housing for my iPhone 6s plus, every thing seems to work fine except for the Wi-Fi signal I think cellular and bluetooth signals are also weakened but Wi-Fi is the most noticeable for me. The only way to get 3 bars is to stand right next to the router. A weird thing is also that I can only connect to 5GHz internet, 2.4 doesn’t even show up. It might show up around once per day or less. I’ve compared my new housing with my old one and they both look the same if the colour is not counted. Thanks in advance for any answers!
Color can be the problem. On the inside face of the case, there are contact areas where the paint is intentionally brushed off to make electrical contact possible, these areas are used for grounding AND antenna feed points. You can submit a picture of the original and replacement case so we can check for sure. Example of a bad case:
A good one:
