JS bridge callback is not always invoked

[sergeys-opera]

I have an app with the following JS bridge setup:

window.momi = {
    callNative: function (methodName, params) {
        return new Promise((resolve, reject) => {
            if (typeof window.momiBridge !== "undefined") {
                window.momiBridge.callNative(methodName, JSON.stringify(params), (responseBlob) => {
                    let response = JSON.parse(atob(responseBlob));
                    if ("error" in response && response.error != null) {
                        reject(response.error);
                    } else if ("result" in response && response.result != null) {
                        resolve(response.result);
                    } else {
                        reject({
                            code: 1,
                            message: "No `result` neither `error` returned from the host"
                        });
                    }
                });
            } else {
                let errorMessage = "No `window.momiBridge` injected!";
                console.error(errorMessage);
                reject({
                    code: 1,
                    message: errorMessage
                });
            }
        });
    },
};

I inject the script on every page load and it works well most of the time. However, sometimes the callNative callback does not get called.
I see, for example, onCallback: 12, ... printed in the console but on the JS side the callNative callback is not invoked.
Note that during the same page session, I do get successful method calls (even for the same failing method). In fact most of the time the JS bridge works, it fails only occasionally.

Is there anything I'm doing wrong?

[sergeys-opera]

For the failed scenario I saw the callback being added in the console:

add callback: 12, (responseBlob) => { ...

And it being invoked later on:

onCallback: 12, ...

However, the callback code didn't run.