No notifications for many observations

Two months ago I noticed that I did not get notifications for some of my observations. The problem got worse since, and now I don’t get notifications anymore for most of my recent observations (same with the website, the dashboard, and the app). What I have to do is to scroll down my list of observations and try to spot if something changed (but this makes it very hard to keep track of changes to the older observations). Does someone has similar problems?