Same issue for me :
(end of) dmesg : [ 376.869641] rpi_firmware_get_throttled: 7 callbacks suppressed
[ 376.869648] Under-voltage detected! (0x00050005)
[ 383.109695] rpi_firmware_get_throttled: 7 callbacks suppressed
[ 383.109702] Voltage normalised (0x00000000)
[ 457.990026] Under-voltage detected! (0x00050005)
[ 462.150046] Voltage normalised (0x00000000)
[ 497.510066] Under-voltage detected! (0x00050005)
[ 501.670056] Voltage normalised (0x00000000)
[ 736.711696] rpi_firmware_get_throttled: 1 callbacks suppressed
[ 736.711704] Under-voltage detected! (0x00050005)
[ 742.951705] rpi_firmware_get_throttled: 1 callbacks suppressed
[ 742.951712] Voltage normalised (0x00000000)