LinkedIn does not recognize thumbnails

Hello

I have noticed a problem in my last two entries. When I try to show them on Linked In (just writing the URL), the website does not recognize the thumbnails so it only shows the text.

Until now I did not need to define a thumbnail properly, but the image i attached to my entries was perfectly recognized. However, nowadays, not even defining the thumbnail seems to work

It’s really wierd because it has worked perfectly until 2 weeks ago.

¿Any possible reason for this matter?

URL: https://www.linkedin.com/groups?home=&gid=2591200&trk=my_groups-tile-grp