They Don't Understand
You are working on a project with a small team. There's an issue that needs to be addressed. You try to explain how you would solve this issue to one of your team-mates. They listen to you and nod as you explain away. Once you're done explaining, your team-mate responds with "I understand".
The fact that they said "I understand" doesn’t mean they understood you at all.
There are three possible states of understanding: 1) you understand something; 2) you don't understand something; 3) you think you understand something but you don't really understand it.
It's that last state that creates misunderstanding.
Misunderstandings inside your project lead to all kinds of trouble. We're talking about missed deadlines, bad budgets, disappointed customers, etc.
The most legendary hotel in Finland, Hotel Kämp, has a workforce with a diverse international background. English is the primary language of communication among the employees. However, very few people are actually native English speakers.
To make sure that the hotel customers get the premium service they pay for, you have to minimize the misunderstandings between employees. Broken English doesn't help. It adds its own set of challenges.
This is how Hotel Kämp makes it work: You tell an important thing to your colleague. They rephrase your message back to you. If something was missed or misunderstood, you repeat the process until you have sufficient mutual understanding. You are not allowed to just say "I understand" and move on.
I'm not saying this is what you should do at your office. In fact, I'm pretty sure a lot of people are going to take it the wrong way if you continuously ask them to repeat what you just said to them.
Just remember that the only way to solve those misunderstandings is to find out what the misunderstanding is and discuss about it tirelessly.
I say tirelessly because it's so easy for the both of you to just agree to understand even if there is no real understanding. I have said "I understand" just to move on in a discussion even when I have honestly had zero understanding.
Most importantly, stop trusting the phrase "I understand." The phrase bears no meaning.
P.S. I don't know if you understood me or not ;)