UPDATE/EDIT: After further testing I have deleted the original text in this thread and can conclude the following:
After extensive testing I have finally nailed down why Fist Over Matter sometimes doesn’t proc Samsara for me. The issue is entirely related to Fist Over Matter and is due to a bug causing Fist Over Matter not to deal any damage to your target unless you’re actively watching it.
I play on PC and don’t know if consoles are also affected by this.
I have made a short video that demonstrates this bug: