MSP432P401R: How to prevent RTC from being disabled in LPM3

Part Number: MSP432P401R

I use MSP432P401R.

I have a question about how the RTC works in LPM3.

I want to realize the operation to exit the LPM3 by the interrupt of RTC.

1. Create a thread_A in TI-RTOS
2. Make pending using sem_wait in thread_A
3. CPU is sleeping on LPM3 while pending thread_A
4.  Exit the LPM3 by alarm interrupt of RTC

After step 3, when checking the register, RTCHOLD of RTCCTL13 is changed from 0 to 1 in RTC_C.

Why RTC is disabled after step 3 ?

Below Table 8-10, I think RTC_C is avalable in LPM3.

I would appreciate it if you could teach me about  causes and alternatives.

Thanks,

Koki