I posted an image on Instagram and enabled an option "Post on Facebook" too. When I checked on Facebook, the post didn't appear on the timeline. I looked into the activity log, I didn't found any update of my recent post. I looked into photos, I found my Image over there.
Best Answer
I would suggest you unlink your Facebook account with Instagram. And link it again properly.
When we reset our Facebook password, Instagram doesn’t log you out from the Facebook account.