Heart Rate icon flashing

Nope. I usually have to wait for the GPS to get a fix, and then I start.

Having said that, I've noticed that sometimes the HR reading is way low at the start of a run, perhaps for a minute or two. Other people have also reported HR drop-outs during exercise. So perhaps it does matter that the HR is tracking properly?

To be honest, until I read your post, I thought "flashing" meant "good to go."

The flashing of the icon I suppose indicates that the variation of the pulsations has not stabilized yet.
In my case, before starting an activity I have to wait between 10 and 20 seconds to stop blinking.

Flashing indicates searching/connecting for sensors. Solid means connected and good to go.

I waited and it stopped flashing and then 3 seconds later began flashing. Va3 was tight, I ignore now, it seems to track pretty well compared to my strap anyway

For running, cycling etc, I use a HRM strap as this is more accurate when the watch moves a lot...due to the type of the band I use.
My watch band is a metal band with clasp, so I can't tighten it more during work out.
The VA3 Optical HR will lose the pulse and report wrong reading (90 bpm when I am actually at 150 bpm!) when my wrist move a lot (again because the band is not extremely tight on my wrist).
The OHR work otherwise perfectly for any other low movement activities, walking and every day/night use.

The HRM Strap (ANT+) connect immediately at the beginning of each activity. The heart logo flash for 1-2 sec at most and then turn solid followed by a confirmation message on the VA "External HRM connected)... Works pretty well and accurately.
I did a sprint and my HR climb quickly/sharply, as expected.