I wouldn't be able to make any good suggestions without some troubleshooting. Before I start, have you checked out this page about connecting to WiFi?
WiFi Guide and Troubleshooter for Tesla Vehicles | TeslaTap
If the 3 has trouble connecting to your wifi, here's what I would do to troubleshoot:
- I'd like to know exactly what "my M3 doesn't seem to like it" means. Did you get an error message? Did the wifi channel show up in the channel selection? What exactly do you see on the screen that leads you to not be able to connect?
- Make sure that your WiFi is setup for WPA2 authentication
- There might be problem connecting to your TP-Link Powerline bridge for whatever reason. Try removing your main wireless router from you home, bring it into the garage and only plug in the power. See if the Model 3 can connect to the WiFi with the router in close proximity.
- Another thing to try and test is to remove the WiFi password temporarily, and try connecting with the Model 3. This could help determine if the issue has anything to do with the authentication handshake.
There's almost no reason for your Model 3 to not be able to connect to your router that's sitting in the same room. If you can connect, then the next step would be to compare the WiFi setting between the router and the TP-Link extender. Good luck.