Pictures turn into grey boxes on the back of the card

Hello, the pictures on my Anki cards are not showing on the back of the card, it’s just a grey box. I found this issue on both AnkiWeb and Anki on my computer. When I try to edit the card the picture is there but it’s just grey when I preview the card’s back. I tried to remove the picture and put it back, delete the cards and import them again as well as update Anki. The problem started when I downloaded the add-on “Image occlusion”.

Did you download this add-on Image Occlusion Enhanced for Anki 2.1 (alpha) - AnkiWeb ?
Try disabling it from Tools > Add-ons and restarting Anki.