Downwind Instability = Swim

I sailed a Radial a couple of times before I got the Europe. The Radial appeared far less responsive to my weight than the Europe - I'm about 62 kgs. I like that fact that if I move around in the boat I get an instant reaction, even if sometimes it's not necessarily with the right outcome. 

Once I can get time on the water that isn't on a Sunday I'll have some things to work on - I'm looking forward it.

One thing I'm not sure was mentioned above was to check the range of movement of your kicker as maybe it can go off too far? A very rough rule of thumb is to put your elbow on the top of the transom, then the furthest the boom should go up is the end of your outstretched fingers. If it can go up further then that may not be helping.

Worth a look at Lars' youtube channel - not that relevant to pond sailing but it's definitely how you sail a Europe well. 

FTFY 

I have seldom sailed such a stable and forgiving singlehander as the H2 downwind; on the day that I raced the demo boat it was seriously windy and even after going "down the mine" the bow popped up.  And she was dead stable on a deep planing run.

Like Keith's Merlin designs, of which I sailed one in my youth, I suspect that the H2 might be less forgiving when allowed to rail on her chines.

The large flat top main may be an issue, but stays don't stop the Solo from sailing by the lee, albeit not as extreme as the non-stayed classes, but it is still fast, and I would suggest sailing deep on the run allows you to pick your gybing moment almost anywhere in the downwind leg, whereas a reach to reach gybe commits you to gybing at a specific point.