Nicolas Well, there are always conservative admins, people who get to know a version well and as a result support their users accordingly. As you may very well know, 80% of the users know only 20% of the features.
In my case, Moodle 3.1 (LTS) is my preferred version. (Yes, I am aware of the May 2019 dead line.) I support your decision to follow the Moodle version, even the minor ones, closely. I am still testing Moodle 3.5 - MoodleBox 2.5 was one of the reasons. I am not complaining, in fact Moodle 3.5 is perfect for a project I have in mind (see https://discuss.moodlebox.net/d/27-a-pool-of-moodleboxes-an-idea), because of Moodle Mobile. But my MoodleBoxes will get stuck in remote places where there is no technical support. Which means, those boxes will stay with Moodle 3.5 for a long time.
But the whole discussion is not important since MoodleBox 2.5.1 is available here: https://github.com/moodlebox/moodlebox/releases/tag/v2.5.1. The point I mentioned earlier was more cosmetic: The fact that https://moodlebox.net/en/news/version-2.5.1/ has a link to latest image, under "MoodleBox disk image" - not to 2.5.1.