[immerlustig]

1 Why did this happen on the shallow dives, when it has never happend on much deeper?
2 How could it happen if I was 0% congested?
3 Any recommendations to avoid?

hi,

1 relative pressure increase in shallow water is greater than at depth meaning air expands faster at the end (top)
2 if your reverse block did in fact occur all of a sudden, without any real warning that would indeed be a very rare situation. sometimes over the period of the dive session equalisation just gets worse slowly. a reverse block is usually also not happening spontaneously but building up over time. you might notice somewhat slower equalisation going down as well as up.
3 paying attention to equalisation (and how you feel before, during and after the dive), diving conservatively to be able to slow down the ascent rate to allow air to expand more easily

anyway, that are some experiences of mine at least.

cheers,

roland