Fenix 5x hr issue

I have a problem with fenix 5x hr I can only read in 90-120bpm when I'm cycling, even though when I'm on the ride uphill usually 170 + bpm but on my f5x  just 130bpm(i have compared with other gadget)... often during not wear it can read hr (see pic)

Software v.25.00

If anyone has solution please help