It seems the matrix server is down:
curl -Lv "https://app.nitro.chat/"
* Trying [2a01:4f8:10b:b1:2::]:443...
* Trying 88.99.240.82:443...
* connect to 88.99.240.82 port 443 failed: No route to host
* connect to 2a01:4f8:10b:b1:2:: port 443 failed: No route to host
* Failed to connect to app.nitro.chat port 443 after 2142 ms: Couldn't connect to server
and it seems BGP routes are also missing according to a few bgp looking glass servers.
mtr -z app.nitro.chat
also fails:
13. AS3257 2001:668:0:3:ffff:1:0:102a 0.0% 39 155.1 156.4 154.8 182.4 4.8
14. AS24940 core23.fsn1.hetzner.com 0.0% 39 158.7 158.7 158.6 158.8 0.1
15. AS24940 ex9k2.dc1.fsn1.hetzner.com 0.0% 39 161.8 162.2 161.5 174.1 2.7
16. AS24940 2a01:4f8:10b:b1::2 2.6% 39 161.4 161.4 161.4 161.6 0.0
17. (no route to host)