Codechef Api giving 5xx response

Codechef Api is giving 5xx responses almost everyday now.
I save the refresh token in my database and refresh my accessToken whenever it gets expired.

But when the server goes down and comes back up, I see the following error while refreshing token.

{"status":"error","result":{"errors":{"message":"Invalid refresh token","code":"invalid_grant"}}}

This only happens after your API gives 5xx for some time. Otherwise, I have tried refreshing it even every hour, it works fine.
But after your API is down, it shows the above-mentioned error. The user gets log out because of this.

Please look into the matter.