YEM: Correct, in Season 4, seasonal decay was removed and your outward facing competitive rank was synced with your MMR, but there was a bug for some players in Season 4, and even in Season 5, in which their ranks were incorrectly impacted by the supposedly removed seasonal decay. However, this should have been permanently fixed starting in Season 6. While its definitely frustrating that this bug unfairly impacted your rank, with the MMR sync change, any games you played starting in Season 6 going forward should result in accurate rank adjustments. I hope this helps.
tumblrgirl: That is definitely a frustrating bug, but luckily, I have recorded previous reports of this bug under the subcategory: Competitive Match Game Score. The list is short, so I’ve gone ahead and listed them below. Unfortunately, there aren’t any known solutions to this bug on the players side, so the only thing we can do is to bump up posts about this issue and hope that a Developer will notice and fix it. Including any evidence, whether screenshots or videos, will be of great help in getting this bug fixed as well. I hope this helps.