It's just me then?
Probably not totally. But while any integration between apps is likely to have some awkward aspects, in my experience running droplets has always been reasonably reliable. You can also test the droplet by exporting files from Lr, and dropping them onto it in Explorer or Finder. Try that.
There has recently been a problem where the droplet and Photoshop couldn't communicate. I can't recall the exact message, but it is fixed in 2015.8 / 6.8 .
yep there was a problem recently which meant it totally didn't work, and then it was "fixed" which meant it went back to what I was used to: working sporadically. I can run a batch from bridge after export, however I'd rather use the functionality that is supposed to be there.
I don't find it works sporadically - it has always worked reliably until I broke something. That's on PC and Mac, calling the droplet both as a post processing step in Export and as an Edit With external editor.
Large numbers of files can cause a problem on Windows. Lr sends the instruction as a long text string including the path to the droplet and to the files. If that string is too long for Windows, the droplet can fail to launch. You can minimize this risk by keeping the file paths short.
Try dragging the files from Explorer/Finder and dropping them on the droplet. It'll help diagnose where your problem is.