They are allright, wrist and chest strap are quite near, wrist hrm takes a few seconds longer to follow HR changes compared to chest HRM.

But!

Wrist HRM are not that good for using on cycling because hand when grips and flexes around will make wrist HRM logic off balance while chest HRM will do job without problem. Add into that dust and sweat and you have slow reading and strange numbers you are experiencing.

So for all kinds of cycing , chest HRM is better choice for accurate readout.

Have Edge for cycling (road, mountain, climb) and exclusively wear chest HRM, but for everything else I use Instinct2 with wrist HRM.