I think we'll need a bit more information to help you with this; specifically, where are you seeing this? In addition to the wiki you're seeing this, is this happening in discussions, or on message walls/comments?

I can show example: https://luntikbackrooms.fandom.com/ru/f/history/pr/4400000000000213194

This message is not deleted

How peculiar. After refreshing my cache, I can see you are correct. Trying to view the history of your post here results in the attached error.

I would have to assume this is an unintended biproduct of the recent failover testing or perhaps some type of attack (due to the nature of the error text). Please report this to Fandom here.

We'll look into the post history error - but just in case others see this and gets concerned about the error message above:

This is simply one of our updated designs for error pages, which uses elements from pop culture. Fallout, in this case. It's intentional design!

I also encountered this for the first time

I don't know

We can't help with this. The only way it will be resolved is if everyone who encounters it sends a ticket with the link in my second reply.

I accessed this post using mobile data, unfortunately on wifi use it's the same error

Just figured out this kind of error had something to do with certain situation at FANDOM as of late: