Yes, it is a problem.

In my opinion, passion is always more important than skill. To put it in an example:
What candidate would you rather have - one that has all the skill but only turns up for the 9-5 and puts the bare amount of effort in OR someone who doesn't have all the skill in the world but researches technologies in their spare time, stays late after the contracted hours etc.

You have to bare in mind however that finding someone who is passionate is substantially more difficult than finding someone with the skills. Being a start-up is being a culture, it's important to hire those that fit in well with the rest of the team - for my company at least, this is the most important thing.

Passionate developers who are not capable will be as good as putting the janitor in charge of a nuclear power plant - he might learn on the job, but the risk of a disaster is huge. On the flipside somebody who's not passionate, but can get the job done will at least get the job done and you'll have a product that can enter the market.

I'd like to vote 'both', because both are crucial as @JanVladimirMostert pointed out. The early days are very important days, when you'll create either a prototype that you can later throw away, but you need creative and capable engineer to build something good enough with minimal resources, and/or you'll create the foundation of your platform, and any small mistakes there has consequences in the long term, so you definitely need capable people. But, since resources are usually constrained, and because you also want a ton of ideas and insights, you need them to be passionate.

Long story short: you'd better hire less, but focus on people who are both passionate and capable as the very first team members! As the team grows later, they will shape the team attitude, the work hygiene, and you'd better have good ones from day 0.

I think you'll find that anyone can be passionate about anything if you assign the person enough value. It's hard for a person to be passionate about working at a company which doesn't treat them well and pay them enough money to live. Passion can be provided by both the employee and employer.

An employee might not want to work on a project. If you make it fun or challenging (in a positive way) or generally worth their while they would probably enjoy working on it and have motivation. Ask them what would make them passionate about the project. It might be as simple as letting them explore a new technology stack that they've always wanted to try out.