I've been using the same setup for about 2 years for my export droplet action. My LR has been acting screwy. I've found a work around to get LR to stop freezing but now when I export LR is selecting the wrong droplet to play on the image files. I've remade my droplet from the action in PS and saved it under a new name and remade my export preset with the new droplet and LR still plays the wrong droplet. If I execute the new droplet outside of LR it plays perfectly so that tells me that something is up with LR. I've deleted my preferences folder and updated LR to the newest version and no dice.
This bug was introduced in CC 2014.4 / 6.4 and Adobe has acknowledged it: Lightroom: Droplets no longer work with export presets (CC 2015.4) | Photoshop Family Customer Community. However, that doesn't ensure that it will be prioritized for a fix in the next release, so please add both your vote and detailed opinion to that bug report. As a workaround, you can either roll back to 2014.3 or use a plugin to run the action directly from your export. See the bug report for details on these workarounds.