Like Tom said, the software gets confused. Dragging can make very wilds decisions that cause other constraints to fail.
Snapshots are hard to deal with during development because they go out of date too easily with every change. But on a stable design, they are nearly imperative. If you want a mechanism analysis to return to a known state, you need these snapshots there as well. All in all, this one tip alone has saved me huge levels of frustration.
The second part is limiting the motion in the assembly constraints. Anytime you use a mechanism constraint, you risk the ability to drag something to their extreme which may not be compatible with another linked components. Typically this happens when a plane "flips" during the motion. For instance, linking chain links can flip onto itself without hesitation just by dragging the chain back and forth (like pushing a rope). Limiting the angle will avoid this clipping degree of freedom. Most mechanism constraints also have the ability to set a regeneration value. This is helpful, but do know that sometimes this gets in the way (can create its own error). This only tries to restore the "default" position when the assembly is regenerated or opened. This ensures the part will always be in a good state. Unlike snapshots, this is more stable since it doesn't just take a ...well "Snapshot". It is an evaluation condition.
If things get out of whack, and regen won't fix it, then try a verified snapshot. Just remember to redo your snapshots often in development! We need a prominent button for "default snapshot update"!
This is what you are looking for in your mechanism assembly constraints:
