(NB SCROLL DOWN TO BOTTOM FOR POSSIBLE SOLUTIONS)
Just a quick post to let everyone know that if you are experiencing a problem with html "center" tags centering your entire document even if there are no errors then it is not you.
It seems that something has been updated and that has broken how the "center" tags work. I just checked through my old posts (which were fine before the update) and they are all showing the same issue.
I have also noticed that direct links to my post no longer work either for me or anyone else. This is my post from tonight and this is the direct link:
https://steemit.com/health/@thecryptofiend/vitamin-d-may-prevent-colds-and-flu
Don't Panic I'm sure the Steemit Team will fix it soon. I have made a github post here.
EDIT -
Weirdly the link for this post works but that old post still doesn't.
EDIT 2 - SOLUTIONS
Thanks to 
for pointing this out some of my tags were improperly formatted with the the heading tag and center tag the wrong way round e.g. center coming first to open the tag, then heading coming first to close.
Some recent changes have made the handling of tags stricter so this may be causing them to not work when they did before.
The only way to sort it right now is to go back and edit old posts where the formatting is broken this way and swap the order of the tags round. It is not perfect but does work.
Also thanks to 
for pointing out that the broken links will work if you strip out the actual topic tag so for this link:
https://steemit.com/health/@thecryptofiend/vitamin-d-may-prevent-colds-and-flu
You would try:
https://steemit.com/@thecryptofiend/vitamin-d-may-prevent-colds-and-flu
It should work that way.