[7th of February 7 am EET] Facebook has indicated that they pushed a fix and posting to Instagram should work normally. Once again sorry for any inconvenience.
[5th of February 21 pm EET] The Facebook engineering team has identified the root cause of the problem and actively working on the fix. Posting to Instagram is working currently, but the Facebook incident report still remains open. We are monitoring the situation and will close this case after the fix has been verified.
[5th of February 1 pm EET] Facebook has dedicated a team to investigate and fix the Instagram issue.
[5th of February 11 am EET] Unfortunately, publishing to Instagram does not work properly. We are investigating the problem and will notify you as soon as we have more information or an estimate for the fix.
More information on Facebook of this Instagram issue.
Sorry for this inconvenience!