I have extensive experience in this realm, including both independently re-deriving Kelly before learning about it and then working extensively with variations of it, in nominally Kelly-optimal conditions. Kelly is only optimal under a very strict set of criteria, and those criteria de facto do not occur in practice. It's a great guide to the landscape, but a terrible perscription in most situations. Common errors include misunderstanding what counts as a bankroll, inability to access large portions of the real bankroll, changing returns to investment size, the existence of limiting factors, having almost any real utility function, unknown unknowns and edge uncertainty which is almost always correlated, psychological impact and inability to precommit credibly to Kelly, outside perceptions and their impact on your bankroll or utility, not accounting for calculation errors, odds or outcomes that are impacted by bet size, and more.

I may write a top-level post going into more detail (feedback on this idea is appreciated), but here I will deal only with this particular case.

In a start-up, the bankroll definition and potential is one key. Your bankroll includes more than you think, and that's especially true in a start-up world where you can, even in failure, get more investment and start again, or join someone else's start-up, or just go back to a day job. Kelly assigns infinite disutility to going broke, and going broke is standard procedure in the startup world. Also, how you take your compensation is largely for motivation and signaling and to keep control of the company, all of which impact the result. In bankroll terms my investing in my own company, and taking $0 other than expenses from my start-up work was madness, but it was clearly the correct play and has paid off handsomely in numerous non-bankroll ways even if no money results!

Going full speed at a startup, even in failure, is often a winning play as you develop connections, reputation, experience, skills and other neat stuff like that, laying the groundwork for future success.