Just a few thoughts:
Perhaps not enough air in the shocks?
Leaky O-rings on the compressor side or shock side of the air hose connections?
If the air is out of the shocks, front & rear, the front end will bottom out on even the softest of bumps & the rear will feel under damped.
I had both the above happen on my '89, replaced the O-rings at the compressor air hose connection, everything was fine afterwards. As added insurance, I installed a set of progressive suspension springs, front & rear. The front springs are designed to run w/o any air pressure & the rear will allow you to run about 10-15 psi less in the monoshock for any given weight setting.
I have heard of one or two Ventures that had a frame weld crack or break entirely, however, I don't believe it's a common issue.
Hope this helps,
Greg
Also, my front end was also quite "flexy" especially in hard corners. A superbrace fork brace took care of that.