I had similar issues with my Xiaomi phone. One reason is that the peering from UPC Switzerland to Singapore is currently extremely horrible. One testsite (Amazon Singapore, where the Xiaomi Cloud is hosted) had exactly 30 Hops in a traceroute. The problem is, 30 is the maximum (default setting in most operating systems), one more hop and the IP/site is unreachable. The major source for this problem (bad peerings) was/is situated somewhere in Asia and out of reach for UPC sadly.
In my tests Swisscom had around 2 hops less which just could make the difference between broken and working.
Not sure if you are hitting this problem though, but it might be possible.