Hey I noticed that if I trim my out drive all the way up to the trailer position if I come back a few days later the trim or outdrive will have dropped all the way down to the original positionI have a bravo three outdrive
Check the level in the trim reservoir in the engine compartment. If it is low then the trim rams are leaking. SEI sells them and they are easy to replace. I have replaced both sides on my I/O. One was leaking ( I would get a sheen on the water behind the boat). With one bad, I figured the other was not far behind. You need a line wrench for the fittings. It is a DIY job.