SoftBank (OTC:SFTBY) has a bold plan to invest $100 billion in U.S. companies through its Vision Fund. Those efforts have not always been smooth sailing with the company stumbling badly with its investment in WeWork, the coworking company that failed in its efforts to go public.

Now the Vision Fund has another high-profile problem. It's losing one of its top U.S. executives, according to a story first reported by The Financial Times.

A man carries a box out of an office.

SoftBank's Vision Fund has lost a top executive (not pictured). Image soruce: Getty Images.

Who's leaving SoftBank's Vision Fund?

Usually, when a top executive leaves a company by his own choice both sides release a bland statement. Maybe they say he wants to spend more time with his family or perhaps "pursuing other interests" is the stated reason.

In this case, Michael Ronen, one of five managing partners running the fund, has quit. Neither he nor the company explained why Ronne, who supervised many of the fund's transportation investments, released a statement but The Financial Times piece said he had "issues" with the parent company.

What should investors watch?

Sometimes people leave companies because they disagree with decisions made by top management. That's not always a sign that the company has major problems but it's definitely a red flag.

When a top executive leaves suddenly, that could be a sign of a deeper problem and that seems possible after the WeWork debacle. Ronnen may simply disagree with SoftBank's top leaders on strategy or maybe he really does want to spend more time fishing.

The Vision fund has stumbled publicly but $100 billion buys you a few mistakes. SoftBank does not have a perfect track record (it probably regrets making heavy investments in Sprint for example) but venture funds don't need to hit on every investment. This departure may be a sign of deeper troubles but that's only a possibility, not a guarantee.