Unfortunately, although LibreOffice has no problem opening the file, it still appears to be corrupted when opened with PowerPoint or KeyNote.
I have to mention that this demo has a bigger dataset and a more complex template.

https://www.dropbox.com/s/j6jsyto4hq6d9ex/still_corrupt.zip?dl=0

When generating a presentation from a template which includes pptxSlides, if the list contains more than one item(at least one additional slide is generated),the result file appears to be corrupted when opened with keyNote or PowerPoint.
The PowerPoint repairer signals that the first slide in the generated slides list is broken, and also, the first item to be replaced by the presentation is not properly parsed(is replaced by blank in all the generated slides), if the item is happens to be an image, the jsreport api crashes.
When I mention the first item to be replaced, I mean the chronological order in which the items were inserted in the slide.
Reproduction of the bug:
https://www.dropbox.com/s/mm48ioamfguu73b/corrupted_output.zip?dl=0

Thank you, now it's working just fine.

When generating a document from a template which contains {{pptxSlides list}}, if the list contains 2 or more objects, the first slide is placed correctly in the presentation, but the rest of them are appended to the end of the document, instead of being inserted right after.
Details: used as nodejs api
You can see a reproduction of the bug here:
https://www.dropbox.com/s/12k1nto9lkijfoy/slides bug.zip?dl=0

Now it works just fine. Thank you!

I also discovered that LibreOffice doesn't get along with KeyNote, as the later one can't open files edited by Libre(PowerPoint and Google Slides have no problem doing this).

https://www.dropbox.com/s/819vicdfjyd1d7m/export.zip?dl=0

Here is everything I used to render my file in the demo.(it requires a local jsreport server to be running and may require some node modules to be installed before it would run properly).
As I said, result.pptx is corrupt because of the leftover group of that unchanged image.

I didn't manage to use the playground to create a demo because I get some 502 Bad Gateway nginx/1.13.12 error when I`m uploading my pptx file, but I recorded a video where I present my problem: https://youtu.be/9PbuYinfsAo
I will try to make the playground demo work by tomorrow to show more concrete proof of my problem.

When I try to generate a report from a template which contains more than 2 images per slide, the output file is corrupt when opened with PowerPoint or KeyNote and for some reason it works only with LibreOffice.
If I have only one image each slide, everything works well.
While debugging this problem I found out that only the images added chronologically on the slide in even positions are not replaced(1st and 3rd are replaced properly, the 2nd and the 4th remain default but without the "{{" text from the template.