Polar own optimizer results

[bubblegum]

the past few months ive started using the optimizer function on my cs600 to take my resting heart values each morning, and the values it spits out have been fairly consistant with training volumes and rest days. but in the last week or so ive started to get values of 4 and 5 (stagnent traning) desptite undertaking rest days. More weird i find is that the values of average and peak HR are pretty much the same as what i was recording a few weeks ago when i got consistantly under 3, just wondering if anyone else has had this issue with the polar cs600, or know how it gets the number value based on the HR output??