Can't edit slideshow with more than 3 slides

Hi !

I've been trying to migrate old slideshows from an old site and I'm running into various issues unrelated to this post. To make sure I'm doing things right, I created a brand new slideshow module with all default options, deleted the 3 default slides and inserted my own pictures, one at a time. After adding 4th picture and saving the slideshow module, the 3 default pictures are displayed again in the editor ! Same happens when adding pics 1 at a time or 4 pics together. Also tried with various pictures of various sizes, seems unrelated to pictures. Also unrelated to captions, no captions in this simple test. Also tried to clear browser cache, stop/restart Xampp (its a localhost), stop/restart PC. I'm running out of things to test !

Setup is as follows :
Joomla! 3.9.18, admin template Isis (default, unmodified)
Slideshow CK module 2.0.17 free version
Firefox 75.0 (same issue with Microsoft Edge)
Windows 10

Did I miss anything too obvious to see it ?

As usual, thanks for the help.

===== added 05/07/20 12:39p =====
Another test on another site with nothing on was successful, with 23 pics added. So this issue is site-related

Hi
ok for "this issue is site-related", because I have never seen this error before
you can try to disable the plugins that you have installed to see if it makes a difference. For sure, the slides manager info Slideshow KC is working correctly since years, so there is something in conflict here

let me know
CEd

Hi !

After more testing, the issue does not look as only site-related, but also template-related. When I switch from isis to hathor, everything works fine. But after reinstalling isis from another site from a clean Joomla! install, the issue shows up again. So far I have no clue on what could be different between isis and hathor.

But there's also something wrong with the site itself, since Slideshow CK on another site works fine with isis !

Isis is the default joomla admin template, I use it on all my websites and I never had such issue
the problem is not related to Isis

is that possible for you to put the website on a temporary server to give me an admin access ?

I agree, I also use isis as default admin template, without any problem so far. I suspect there must be something between the site itself (did I corrupt anything while tweaking the DB ? could be ...), some isis feature (when I switch to hathor everything works fine), but which one ?, and the original install (not a pure Joomla install - an AS package including Joomla and perhaps a dozen extensions). So what I'm doing right now is reinstalling a second test site from a pure Joomla! package, reinstalling all extensions including Slideshow CK, migrating everything from test site #1 to test site #2 (in progress ... its 46 gigs to copy). So far Slideshow CK works absolutely fine. I'll see if I start to see issues again, then I'll know where to look at.

Accessible test site is unfortunately not an option, site is waaaaay too large ! Too bad, I would have loved to give you access, just to see.

ok great, if you are able to create a new website that works, this is great !