Breathwork "brpm" inaccuracy?

So it was some 20 minutes before my sleep and I decided to do some breathwork for fun. I did Coherence for 8 minutes and then found my brpm to be 4 (ignore the stress change), which is way too low. So I did it 2 more times to see if it was an error, but it was the same brpm for all 3 activities. But once the activity was finished, my respiration rate was 12-15 (check 2nd image). The lowest I have seen is 8 brpm, but 4 brpm while sitting straight and taking deep breaths in and out seems erroneous to me. Has anyone else experienced this or am I missing something? Btw I am using Venu 3 and on firmware 8.25. I did breathwork activity in previous firmware 7.07 and found the brpm to be the same 4 (just rechecked).