Ok bit old - but only 2 weeks
Does it actually get to the floor then magically open later - or does it reverse during operation?
If it's reversing during operation - probably a combination of needs a bit more force (ie you probably need it serviced) - or photoeyes are just a bit off, and the track twists a bit causing eyes to loose sight of eachother...
If it's just randomly opening - Disconnect the wall button from the opener (depending on vintage, it'll be a screw terminal with a red square beneath it - or a push to release clamp style that's also red. See if that resolves it - if it does... Congratulations - you've got mice, or a staple shorting that wire... Rerun a new wire.
The other 'new' random opening scenario of late - is the new chamberlain security+2.0 remotes have been seen to magically open some older openers.