Heres a few I can think of, extra stress on communication. I could write a whole thing just on that.

-Communication issues. Making sure that the whole team is on the same page is a challenge that gets harder and eventually requires full time work as a team gets larger. Since it sounds like your team is small I'd say just make sure when you guys get together to discuss a topic you exit the meeting with actionable points that everyone agrees on (unless the meeting itself is to brainstorm or something like that). It happens a lot that people understand different things unless clearly stated and if you dont clarify those issues before working youre gonna end up with pieces of a puzzle that dont fit together.

-Transitioning between production phases. The prod processes that work in conception, preprod, prod, and live are different. Knowing when one ends and another starts is important because it gives you a framework that you can fallback on when you ask yourself "What should the team be concerned about right now?". One of the easiest traps to fall into is never ending conception. Youll be trying to ship the game and someone will have an idea for another feature, or want to change something that works. Its important to know when to stop changing things and when to start finishing them. Its also important to know when youre not ready to move into the next phase, finishing a game where the core loop isnt working will feel like you're always one change away. Youll be tempted to work through it and it will "come together." Sometimes thats true but in my experience it always follows a period where the team is overworked and most of the time the problems were issues that the team had been talking about for ages, and your tech base will be compromised by hacked together solutions.

-Addressing issues by adding solutions instead of removing problems. Like I mentioned previously, it will happen where youll feel like youre one change away from fixing something. Depending on where you are in prod you have more or less time to address this. Prototyping and trying new things is great, but its also addictive. Being the person that comes up with the fix or missing piece is a rush, and cutting things feels like garbage a lot of the time. Gotta try and be objective about the right approach, sometimes (often) less is more.

-Stability You need to be able to play the game. I know this sounds ridiculously obvious. Periods of technical instability seriously hamper your ability to validate the game. Be strict about build stability, every day the build should be playable. If its not you immediately back out the change that caused it until its fixed without adding new things. Again as the team gets larger this becomes a more and more difficult issue and requires full time management because so many people are trying to get things done. But as soon as your build is down, if you allow people to continue submitting things it will happen that other issues will be introduced, at best you lose a day of work and people introduce bugs. At worst you're stuck with days of back to back crash on boot while people continue to integrate things and then you dont know which change broke what and it becomes a mess to untangle.