volvo DP outdrive trim issues

[Freebee]

As I have not run the boat for some months, tonight I ran the engine and the drive whilst moored alongside. when put into slow astern the drive popped up and broke the surface. I was able to raise and lower the drive via the trim pump, but each time reverse was engaged the drive broke the surface, what should I check?

 

[Frontier]

I think there is some sort of latch, I remember seeing it when the boat was out and the legs were being serviced.

See here item 47