Unexplained or documented TESTNET FUTURES account behavior

A few hours ago (around 1:00P Eastern time US) I created a TESTNET futures account. As expected, it had an opening balance of 100 000 USDT.
I obtained the API keys, and placed some orders (which were filled) and monitored results in the User Data Update event stream.
There also were two open orders to sell a small quantity of BTC.
A few minutes ago (a little after midnight UTC), there was an ACCOUNT_CONFIG_UPDATE event, which reduced the USDT margin balance to 10 000 USDT (wiping out not only the original 100 000 USDT, but also the small profit made on the test trades). The open orders were also canceled.
I did not expect this, and have seen nothing in the documentation to suggest that a TESTNET account would be modified so quickly (the documentation indicates approximately monthly the accounts are reset ).
I realize TESTNET only very approximately tracks the real market, but should be no reason that it is not stable with respect to externally induced (i.e., by Binance) changes to an account. I want to do as much testing of event handling as possible on TESTNET, without having to deal with obviously bogus changes.
In summary, I would appreciate some guidance on what to expect or not expect on TESTNET.

The testnet could be less stable than the production as we may need to upgrade or reset the environment for better delivery. thanks for your feedback.

OK, but why after reset is the balance not the original ‘pretend’ balance? Why is it reduced?
And, was the reset at ~00:00:00 UTC a ‘planned’ reset?