Pre-market trading refers to trades which are made before the regular trading session (9:30-16:00 ET).
If your stocks are undergoing corporate actions such as split/reverse split, trading may be prohibited before the corporate action is processed, and it will generally resume after the opening of the market.
This is the normal handling mechanism of the industry, and Futu shall not bear any responsibility for the losses caused by it. Although the time for brokerages to enable pre-market trading is not exactly the same under this scenario, Futu will try its best to ensure that all corporate actions are processed as quickly as possible to prevent your trading from being affected.