I've not had any problems with my Mi scale and it's quite accurate compared to another older one I have at home.
But it is interesting that yours failed just when Xiaomi released a new version 2 . Maybe they send a wifi command out to bugger up all the scales so that everyone goes and and buys version 2. But anyway, only $99 is a great price and just throw it away and get a new one!
A simple test of the accuracy is to step on it *with* and *without* holding a 5kg sack of rice.Subtract the two readings.
Even if consistent within one session, it may drift between sessions due to temperature, humidity etc.
Depending which part of angle I step on. I get different results too. Typical Chinese quality.
2 kg bag of rice showing as 4 kg!