For two days, I am not receiving inbox messages any more for comments that were posted after my own comment on questions / answers that aren't my own. I know about the follow-up comments because I checked the posts for updates myself, but I was never notified about them. Let's call them 'type a' comments for future reference. I just did receive a message for a comment that was posted under one of my own answers. Let's call them 'type b' comments for future reference.
I have a feeling that this has something to do with the new follow feature, as I started to use it at the time the messages stopped comming in. The last two messages in my inbox I received are about 'type a' comments posted under a question that I also followed. Since in that case, you would normally receive two messages about the same comment (once, because it's a follow-up comment, and once, because you follow the qestion / answer), this behaviour was apparently fixed. Could this also have accidentally deactivated all inbox messages about 'type a' comments on posts that I don't follow?
As a side note, but probably unrelated, my mobile app now crashes when I try to open my inbox, but appearently, there is nothing much that can be done about it.