[15th of March 1 am EET] Facebook has indicated that they pushed a fix and posting to Instagram should work normally. Once again sorry for any inconvenience.
[14th of March 4 pm EET] Unfortunately, direct 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.
Publishing to Instagram using notifications works normally.
Sorry for this inconvenience!