Chosen Solution
Recently I had my housing changed, so I don’t know if it affects it but it’s not as good as original quality because I bent my previous one on accident. But the wifi was fine until I dropped it from my pocket onto the ground in sitting position, then the wifi stopped functioning normally. Now the wifi strength is so weak I have to be close to the wifi modem to use it and it will also not receive the best strength.. Is there a possibility for the wifi antenna or other component to become loosened? Sorry I am a total amateur to this, because I find it hardly convincing for the parts to be unsoldered for dropping at this height. And how do I know which wifi component do I need to test before replacing it? And I noticed there is a similar post to this which is mainly concerned for iPhone 6, I don’t really know if the components are usable for iPhone 6s Plus so I had to post another one.
Your problem could be related to the drop, the wifi antenna could be detached from the logic board or be broken. Keep in mind that in this phone apparently there are 2 type of antennas (wifi/bluetooth and wifi diversity antenna) Here you have a picture of the diversity antena and a link to buy one
And here you ave the wifi/bluetooth one and a link to it
You have a guide on iFixit for each one Diversity antenna and the wifi/bluetooth antenna And for the last part: the wifi antenna on the iPhone 6 is not compatible with the 6S Plus
