yes he's tricky.
there is a gauge who indicates if doldren can materialise or not.
the gauge take little time to fills up when doldren is near a living creature and the gauge quickly empty if he is not.
you can only materialise when the gauge is full.
but doldren suffers a bug sometimes which makes him materialise on random spots with crazy cam movements.
for players who see you, i don't think they see you, just they are waiting for you because you must be too predictible.
but, your body can be seen when you are in astral cause your stress is full.
and moreover when you materialise you do a specific sound who warn aware opponents, and, (if ping is good and when lock system works correctly...) let them time to react and counter you.