It seems that it's simply impossible to run too many things in parallel over ADB on a single device. Really weird stuff happening, like completely unrelated shell calls using files created by other shell calls. Switch back to serial implementation.

lib/roles/device/plugins/display.js

@@ -2,7 +2,7 @@ var syrup = require('syrup')
 
 var logger = require('../../../util/logger')
 
-module.exports = syrup()
+module.exports = syrup.serial()
   .dependency(require('./http'))
   .define(function(options, http) {
     var log = logger.createLogger('device:plugins:display')