HRM pro plus bad readings

Anyone notice that even if it seems to work, it’s not giving reliable readings? It’s about 1 years old I think, but used a lot.
Around 5000km and a few battery changes.
It seems to be either to low or to high, usually to high, but still not so strange that it shows big spikes or so, just consistent high readings often, which affects Garmin VO2max for instance by a lot for a while now. I don’t think that my vo2max shrunk by 6 points in a few months, with the same training.

last time I had to exchange the hr strap, it poor readings showed on breathing rate, all the data there disappeared, and the hr kinda just filled in the blanks. But now it’s not really showing the same symptoms.