Nextgen bulk optimisation tool doesn't work

– yes
– the optimization menu appears at the top of the page, but eio.js does not appear in the source code of the page.

So, from what you’re saying, it sounds like there is NO Bulk Optimize item in the Gallery menu, is that correct?

Couple things to check here. In the ewww-image-optimizer-cloud folder, we need to edit common.php to allow us to find some more information here. On about line 44, you’ll see something like this:

//add_action( 'contextual_help', 'wptuts_screen_help', 10, 3 );

Remove the first two slashes, which will activate the function below that. Then on your NextGEN Manage Galleries page you’ll see a little Help button at the top right. Click that, and it will display some “screen information” which includes hooks and the like. Please take a screenshot of that via any image sharing site you like and post the link here.

Lastly, are you using any other NextGEN plugins and/or NextGEN Plus?

No, this is wrong: the menu is present; I optimize and click and the menu appears (see screenshot); the page is refreshed but no image is optimized.
I use Nextgen Plus

Sorry, screenshot here https://imgur.com/KSsaabI

And the screen information

The problem is largely solve: optimizing works with the general menu of NG, left / but it does not work if I only want to optimize a particular gallery with the menu “Manage galleries”. But this is not very important.

For posterity, the issue was a javascript conflict with a premium theme. pitou has contacted the theme developer for a resolution.