Conflict with Meow Gallery and Lightbox plugins

[ThailandeAsie]

• [x] I've read and understood the contribution guidelines.
• [x] I've searched for any related issues and avoided creating a duplicate issue.

Please give us a description of what happened.

Strangely enough, this is not just one plugin that makes this bug happening, because wether it's Meow Gallery OR Meow Lightbox plugin active, the slug in the Google Preview snippet from Yoast is marked as "undefined".

See the capture screen here : https://ibb.co/MgCBFD5

Please describe what you expected to happen and why.

By default I should see as expected the default slug as entered in the normal Post or Page area (which normally correspond to the title).

How can we reproduce this behavior?

1. Since I'm not sure which part of these tier plugins create the issue, I can only tell you to try activating one of the two mentioned plugins from Meow while Yoast is activated, doesn't matter if there are other plugins activated or not and not related to theme either.
2. Create a page or post and check the Google Preview area, slug will be empty in the area you can change the preview.

Technical info

• If relevant, which editor is affected (or editors):
• [x] Classic Editor
• [ ] Gutenberg
• [ ] Classic Editor plugin

• Which browser is affected (or browsers):
• [ ] Chrome
• [ ] Firefox
• [ ] Safari
• [ ] Other

Used versions

• WordPress version: 5.5.1
• Yoast SEO version: 14.9
• Gutenberg plugin version:
• Classic Editor plugin version:
• Relevant plugins in case of a bug:
• Tested with theme:

[Djennez]

@ThailandeAsie thank you for the report. I checked it out and the only thing I can find is that, as long as the slug is empty, the snippet preview shows "undefined". But as soon as you add a title, the slug updates and the "undefined" gets overwritten. Functionally, nothing seems to be broken, it's just a slight visual bug when creating a new post. Possibly caused by some javascript overlap.

If you're not experiencing any functional problems (the slug field is supposed to be empty as long as you've not entered a title yet), I am going to close this as it's too trivial of an edge case to look into further.

[ThailandeAsie]

I forgot to precise that when doing this test, I did add a title to the article/page and saved it as a draft prior to check the preview. And so on my side, it says "undefined", even if the title is already prefilled... If deactivating the plugins mentioned above, the slug is then appearing as expected.

[ThailandeAsie]

@Djennez I got some news about this issue. After checking with the creator of Meow plugins, we did a test on a test site. To get this issue, need Yoast plugin activated, one of his plugin, either Meow Gallery or Meow Lightbox AND Classic Editor ! Both 3 plugins activated I do have this undefined slug on the Google preview area.

The author asked me then to give you this question, related on to how you compile js :

When you compile your JS files for your plugin (Yoast), are you using WebPack? If yes, are you using a specific jsonpFunction in your WebPack settings?

[ThailandeAsie]

@Djennez did you see my comment ?