DO NOT SPLIT IT. If you split after applying a velocity envelope, the "right half" will begin with the frame as if the velocity had never been applied. That will cause the jump you are seeing.

When I use velocity envelopes like this, I render on a different track THEN I can split where I want in the rendered clip. Quickest workaround I found so far...

This is a little thing I don't like with Velocity envelopes: this "jump" behavior. I think it should give you the exact effect you want without repeating the clip inside the event on timeline.

Have you ever stopped to consider that it may not be possible to give you the exact effect you want?
At 10% of normal you need to be shooting at 300fps to get the same temporal resolution, as the envelope approaches freeze you may well be asking for a few frames at 1%, that means ideally they should have been shot at 3000fps and at any price theres not much that'll shoot at that speed. Somthing has to give, there's no magic solution to these problems, the miracle is that Vegas does a half decent job with this kind of thing at all. That it gets tripped up a bit is hardly surprising.
Here's a few tips:
If you know you want to slo mo a shot, try to use the fastest possible shutter speed to reduce motion blur. If you ramp down to a freeze, grab the last frame, de-interlace it in PS or whatever and replace the last frame with that and extend it for as long as needed.

Oh... I'm not really into these specs but I get the idea, lol !

What I usually do anyway is cut the clip into several pieces and stretch those from a short stretch to a long stretch (from second split to the last one) then I'd just use your solution for a final freeze. It's even quicker than pre-rendering Vel.Envelopes most of the times.

And I check the oversample switch of these clips...