MSP430FR5994 SVSH Interrupt from LPMx.5
Section 2.2.4 of the User's Guide says:


  LPM3.5 and LPM4.5 can be configured with active SVS (SVSHE = 1) or with SVS disabled (SVSHE = 0). Disabling the SVS results in lower power consumption, whereas enabling it provides the ability to detect supply drops and getting a "wake-up" due to the supply drop below the SVS threshold.


and:


  the "wake-up" due to a supply failure would not be flagged as a LPMx.5 wake-up but as a SVS reset event.