Had the same issue this morning when I wake up and I tried everything… delete app, delete integrationss, delete cache, data, token… nothing helped until, I changed the phone wifi to 2.4ghz service line. BAM worked like a charm! WTH?
edit - Error occured again, but I find the problem. I setup a home assistant at my friends house and nabucasa thinks I tried to connect it, so two servers collide when app tries to connect local server. Disabled the cloud connection on the other one and works like a real charm this time!