We have historically enjoyed the Collection Extension for MediaWiki in our internal wiki, it has been very useful.
Recently we installed another MediaWiki in a dedicated hosted server, we use it as a manual for one of the software packages we develop, so your Collection Extension is a must. Unfortunately we have not been able to make it work properly, the extension does not render the images in the wiki. We have gone through every line of instructions and tested each step, we even made a clone of this new wiki to the hosting service of our internal wiki where the collection extension works fine, and still not working. We compared configuration line by line to the working wiki, we tested all types of image formats and with and without https, etc. and nothing, in the new install it just does not render images, it creates the pdf perfectly with all the other content, but not images.
We tried in the clone test site giving 777 permissions to the image folder and many other things, nothing.