I noted the same just yesterday. Very irritating.
Good to hear it's not just finger trouble on my part.
I have had a similar issue where intermittently right-clicking will no longer bring up contextual menus in layout mode. I have to quit Filemaker and relaunch to rectify it.
It seems to happen when I am working at a pretty steady clip, doing a lot of clicking around the layout objects in rapid succession. It feels to me like I am "in a groove" and just then Filemaker says, "Woah! Slow down there! I can't keep up!"
Im having the same time, this happens once a day for me. But I cant really see what triggers this