In the juicebox gallery we can see all the images in the thumbnails area but the small images don't show in the gallery.
If I check the available sizes for the 2nd and 3rd images in your gallery (which are not displayed in your gallery) in the Flickr flickr.photos.getSizes API Explorer, I see that the only sizes available are Square, Large Square, Thumbnail, Small and Small 320; no regular Medium, Large or Original sizes are listed (the Large Square size only has dimensions of 150 x 150).
Juicebox-Pro can display only Medium, Large or Original size images and, unfortunately, your small images have none of these sizes available.
I expect that if you select Original as the Flickr Image Size but there is no Original size available, Juicebox-Pro will fall back to the Large Size (and failing that, will fall back to the Medium size). However, being that none of the three usable sizes is available, then the image does not display.
The 1st and 4th images in your gallery (which are displayed in your gallery) do not have an Original size but they do have a Medium size and a Large size.
Just for a point of reference, I checked one of my own Flickr images and the available sizes are: Square, Large Square, Thumbnail, Small, Small 320, Small 400, Medium, Medium 640, Medium 800, Large, Large 1600, Large 2048, Original.
Unfortunately, there's no way to modify Juicebox to display other sizes so the only solution would be to upload larger images to Flickr and ensure that there is at least a Medium size available.
Using the same jbcore i use in my pro version, in my other site https:espirito-de-aventura.com, the plugins stays in Lite version.
Please double-check that you have uploaded your Pro 'jbore' folder to the correct location on your web server (overwriting the stock Lite 'jbcore' folder in the plugins/WP-Juicebox/ folder).
There is only one 'jbcore' folder that is used for WP-Juicebox and all its galleries so, as long as the Pro 'jbcore' folder is in the correct location, all galleries have no option but to be Pro (as there will be no Lite files anywhere that could possibly be used).
WP-Juicebox - Upgrading to Juicebox-Pro: https://www.juicebox.net/support/wp-juicebox/#pro
If this does not resolve your problem, try clearing your browser's cache in case your browser has somehow cached and is using older Lite files from a previous version of your website.
Please let me know how you get on and if I can be of any further assistance.
Thank you.