I don't think it's the UniFi connection per se that's the problem though. I mean, loading facebook on my desktop is fine. But on the facebook app on my phone, my feed takes ages to load, and images never appear. Phone notification don't appear too, even though when I load Chrome on my phone to surf everything is fine. Which leads me to believe there is something wrong with the router provided by TM.

Did you just recently subscribe to Unifi? Or was it a sudden issue that just occurred?