The Lumintop GT Nano is my only NarsilM light, so my experience with NarsilM is limited, but the behavior your Sofirn SP36 with NarsilM exhibits (whether normal or not) may be related to the NarsilM battery LVP (Low Voltage Protection) function.
The below quote is from forum member "Tom E" (who developed NarsilM):
https://budgetlightforum.com/t/-/45888/172
Before and immediately after the blinking occurs, you could use the NarsilM (triple-click) "Battery Check" function to determine what voltage the light thinks the battery is at when this behavior occurs (and compare these values to the actual battery voltages as measured with an accurate external volt meter) to ensure that the LVP for your light is working correctly (assuming each of the three batteries in your SP36 functions adequately with acceptable battery internal resistances to provide the current necessary to sustain the selected output).
The LVP blink warnings and main LED output reductions should start occurring at about 3.0 V, with the main LED shutting off at about 2.8 V.
Also, be aware that the voltage for older or inferior batteries (even charged older or inferior batteries) can drop substantially when a load is applied to them (and their voltage can also quickly recover when the load is removed).