Copter-3.5.5 has been released. The official blog post is here so I won’t repeat the message.
In short, the biggest change in the new release is for the new Here GPS/compass modules. If you were using Copter-3.5.4 and found you had to set the COMPASS_ORIENT to “26” to make it point in the correct direction then when you upgrade to Copter-3.5.5 that COMPASS_ORIENT will need to be set back to zero.
I did the update but I still got some issues with it. If I am starting up only on Batterie it do get bad optflow health, but I do get some values on opt_m_x and y. Does it mean that the flow sensor should work?