Any open position can be closed by the IBKR Liquidation system when an account is in a margin deficit. To avoid a Liquidation a Reg T Margin account must have positive Excess Liquidity at all times and Positive SMA starting at 15:50 EST which is the start of the Reg T check period. A Margin or Portfolio Margin account must have positive Excess Liquidity at all times. A Cash account must have a positive cash balance at all times.
You can monitor your account's margin compliance in real time in the Account Window in TWS, on the Portfolio - Positions page in Client Portal or on the Account-Funds screen in IBKR Mobile.