It appears that a malicious user has gained admin access to youtrack and is editing issues and posting strange content Example: https://youtrack.jetbrains.com/issue/KT-56644

checking

Another affected one https://youtrack.jetbrains.com/issue/KT-56645

Doesn’t look like they have any kind of admin access. Seems just like a regular user posting updates. The updates posted on the issues are just comments

even the second one where it appears they’ve just added an image to my description without adding their own comment?

Yep. That’s just a comment with no text. You can add attachments in comments. But yes, for sure, no admin access. Just a regular registered user. They’ll be banned.