I bought a Frorerunner 620 together with the latest HRM six month ago and everything worked fine until about two weeks ago.
I washed the strap as per instructions (ues, I took the monitor off before), but now the monitor reports incorrect/or sometimes no HR.
As my wife has the same watch I used her strap and everything is ok, so it's definitely the strap.
Have reset the strap by putting the monitor in upside down, so not sure what else I can try.
Have always been very careful not to bend the strap.
Thanks,
Leo