The market volatility bit is kind of a reach I'll admit
This is exactly the kind of thing people switch cpa's over, no question about that. But I'll tell you from a practitioners perspective when I hear new clients telling me what the last guy missed I often think 'yep I can see how that would happen'. Doesn't excuse it of course.
These kinds of things are why good practitioners in any service industry work hard to provide great all around service. If something gets missed you hope the client still finds value in your service and you keep them.