Rx enable signal is needed to choose between the bypass path and LNA path. During reception, LNA is enabled with normal polarity and LNA is disabled with inverse polarity and uses the bypass path. The polarity of this signal will be configurable through the LNA_CTRL_POL bit in the BLE_BLESS_EXT_PA_LNA_CTRL register.
The ENABLE_EXT_PA_LNA bit in the BLE_BLESS_EXT_PA_LNA_CTRL register is the control for external PA/LNA control. When this bit is set to 1, enables the external PA & LNA.
Ok so correct me if I'm wrong, but this means there will be cases where the chip is trying to receive and RX_ENABLE is low because it wants the bypass path (presumably because the AGC wants less gain). Also CHIP_ENABLE will be low in this case.