D2 Delta PX - Power save timeout message while flying? - 5.40

I've noticed an issue with 5.40 whereby the Fly activity starts when I begin flying, but after some time, I get a message about a power save timeout. I cancel the message, and the Fly screens remains on the watch, but on the last flight, it didn't record anything. Looking at the documentation, the power save option seems to be related to when the watch thinks it's waiting to start an activity, but clearly it's figured out that I'm flying as it automatically start the Fly activity. So, what's changed, and how do I fix this? I'll need to test it again on my next flight, but could it be that the Fly app is started, but for some reason I now have to start the activity? If I'm right in this assumption, then I never had to do this previously, so I hope there's a setting or a fix coming if it's a firmware issue. Has anyone else experienced this, or have a solution? TIA.