This program runs OK on desktop, but on Android, data reappears in the queue after it's been removed and processed.

main.py

import sys
from queue import SimpleQueue
from threading import Thread

from kivy.app import App
from kivy.clock import Clock
from kivy.logger import Logger
from kivy.uix.label import Label


DATA = [[], [], [], [], [], []]


def subthread(inq, outq):
	it = iter(DATA)
	while True:
		inst = inq.get()
		if inst[0] == "echo":
			outq.put(inst[1])
		else:
			outq.put(next(it))


class TinyApp(App):
	def on_start(self):
		self.inq = inq = SimpleQueue()
		self.outq = outq = SimpleQueue()
		thread = Thread(target=subthread, args=[inq, outq], daemon=True)
		thread.start()
		for i in range(6):
			inq.put(("echo", ("begin", i)))
			inq.put((None,))
			inq.put(("echo", ("end", i)))
		Clock.schedule_once(self.read, 0)

	def read(self, *_):
		outq = self.outq
		for i in range(6):
			assert outq.get() == ("begin", i)
			got = outq.get()
			assert isinstance(got, list)
			got = outq.get()
			assert got == ("end", i)

		if outq.qsize() != 0:
			msg = "outq should be empty, but isn't. Here's what's in it:"
			Logger.error("outq should be empty, but isn't. Here's what's in it:")
			while outq.qsize() != 0:
				got = outq.get()
				msg += "\n" + repr(got)
				Logger.error(msg)
			self.label.text = msg
			return
		Logger.info("Everything worked")
		self.label.text = "OK"

	def build(self):
		self.label = Label(text="Working...")
		return self.label


if __name__ == "__main__":
	Logger.setLevel(10)
	app = TinyApp()
	app.run()