Can’t reattach rail onto Hunter Douglas bracket

My bedroom window has a Hunter Douglas Vignette shade. Since I bought thr place the shade has fallen occasionally and it's always a pain to get back up. Is there a trick to reattaching? Right now one is solidly in, two are loosely in. First picture is secure, second is not.

It doesn't seem to be about force, but finesse. I'm afraid the lightly attached bracket will fall again tonight, or even worse in the middle of the night.

Thanks for your help.

Edit: I found the manual online (should have been an obvious first step but I didn't even know it was Vignette until just now). It shows a rotational action to get the piece to snap into place. In the meantime it's firmly wedged in there and won't come out, so it's good for now, until it falls again, at which point I'll try to fix it properly.