When friends block all communication tools

Before I moved to Japan permanently I had spent a year as an exchange student in Japan. After the year was over I moved back to Germany to finish my studies and came back to Japan after graduation. During the year at the Japanese university, I found a few Japanese friends. At least I thought they were my friends. We stayed in contact through e-mail and social media while I was in Germany and I even stayed at their places when I went to Japan for vacation during the semester break. 

When I moved back to Japan after graduation we were still in contact and also met up from time to time. It was mainly a group of four girls. After a while, I realized that the other three started excluding me. They stopped inviting me when they planned activities and ignored my e-mails and messages. I asked them why but I either got no answer at all or answers that didn't say anything concrete, which is quite typical for Japanese people as they want to avoid conflict.

When I would randomly meet them at events we used to go to together they would straight out ignore me.

I was quite shocked as I didn't know what I had done wrong. From my point of view, I was trying to be a good friend and did nothing bad to them. I really wanted to know why they suddenly decided to ignore me. However, I never got an answer to that question. In the beginning, I was pretty sad as I had just lost three friends. After a while, I started to realize that they might not have been my friends all along and I decided they were not worth being sad about. At that time I thought that I was just unlucky and had met the wrong people, however, a few years later a similar thing happened. 

Through a project I had been working on, I had met a Japanese girl close to my age. We got along well right from the start and after a while we would be texting with each other every day and also hang out together on weekends. Without any substantial change in the relationship, from one day to another, I was blocked by her on all platforms and had no means of getting in contact. 

Again, from my point of view, I hadn't done anything wrong and was again left wondering why someone suddenly decided to ignore me.  

At this point I was starting to think that such behavior might be common in Japan.  I did some research and found similar stories from foreigners with Japanese friends. I am still not sure though whether this is something that also happens in solely Japanese friendships.  

I understand that friendships do not last forever and that people might not want to keep in contact with each other forever, however, until I moved to Japan I had experienced this only as a process of slowly fading out or when it ended suddenly there was a good reason for that. The experience of a friendship ending so suddenly without knowing the reason was completely new for me. 

Intercultural friendship is probably not easy as some things that we do without thinking about it might be weird or even hurtful for the other person. However, sometimes you need to help the other party understand what they are doing wrong. I wish Japan will become more open about intercultural friendships and relationships in the future. 

Have you had similar experiences with a friend from a different culture? Did you find out the reason? I would love to hear about your experiences.