I had the same problem which was caused by the CSP directive blocking the image

Refused to load the image '<URL>' because it violates the following Content Security Policy directive: "default-src * 'unsafe-inline' gap:". Note that 'img-src' was not explicitly set, so 'default-src' is used as a fallback.

So for me a work around without reducing the CSP was to simply set the webkit-mask-image to none for the class dialoug-container

.dialog-container {
    -webkit-mask-image: none;
}

In the docs for Ons-Navigator it makes mention to using swipeable ="force" to enable swipeable navigation on Android at yet it does not appear to work either within the example on that page on an actual Android device. The only place I have found with a working example is this codepen https://codepen.io/asial-matagawa/pen/owRWjO/ but even that doesn’t seem to work if you copy the ons-navigator attributes over to the example on the official page so I was wondering if this feature was added and then removed and the documents were simply not updated to reflect this?