I have the same exact issue with image.manual but the provided snippet does not solve the problem for me (unless I'm using it wrong). When the page is refreshed a few times and it says "No tasks available", the input stream to this function (which would come from the preprocess.fetch_images or loader.get_stream in case of image.manual) actually has reached to its end. This means that get_stream in the snippet, just keeps looping in the while True loop.
Now, if I change the snippet to re-create the stream when it's fully traversed as follows, it does not stop even after all of the images are traversed.
def wrap_stream(source, api, loader):
while True:
stream = get_stream(source, api=api, loader=loader, input_key='image')
stream = fetch_images(stream)
for task in stream:
yield task
Still trying to fix this, but also would appreciate any pointers.