APM:Plane 3.5.3 released

Hi,tridge,
I found that it’s more difficult to maintain the auto flight altitude in 3.5 that that in 3.4,is it?
I truly need your help.My plane cann’t maintain the alt in auto mode,firmware 3.5.3.
I have reported the problem here.Is it a problem only happening in 3.5?
Hoping your reply.Thanks!