Dealing with a slow moving project as a professional researcher

First, I'm not from your area and I don't know how things usually work in medical labs. But I have participated in several research project in field of computer science. Some of these projects were just as you described, and even though the fields are different, I think the situation is the same.

My simple suggestion is to leave that lab for good. That might be a very bold decision, but unfortunately people like you (and me) have to take this bold decision for a brighter future.

You have mentioned that the lab environment is very good, you love your boss and your collegues. That is great! But that is not enough. Simply put, the things you have done goes in your CV. Not your good relationships with your boss and collegues. As a person who is at the beginning of their career, you should activate your potential before it is long lost.

I recently moved to another country from my hometown. And that was not an easy decision. Just like you, I had very good friendships, and perfect relationships with my supervisors. Thus, most of my relatives told me that these type of friendships are not to be found abroad, and I was gambling by leaving such a good environment.

They were right. I do not have very close friends in my workplace here. We do not usually go out for a few drinks occasionally as I did with my collegues back in my hometown.
However, I found two things way more precious in my new workplace. Shared ambition and productivity.

I still do the job I love, I have good relationships in my new workplace, I have a great and friendly boss, and I actually work!

To sum up, every single research project I have participated was exactly as you described. Despite the good relationships and laughter, lack of productivity and drudgery work made me feel like I'm wasting my life there. I realized that I was not happy. I moved on. I'm happy. If you prefer being productive for the expense of slight decrease in the close relationships environment, realize that you are not happy. You should move on. You will be happy.

Also, if allowed, I suggest you also ask this question in Workplace.SE.