「PSA TO THE MAX YA’LL」
As this post says here, Tumblr is, for some unknown reason, wiping out all customizations of themes at random. I still haven’t seen anything saying what the cause of it is, or even what can be done to prevent, and I have yet to figure out a good way to prevent it myself other than backing up HTML on pastebin or in notepad. However! I have discovered a very easy way to recover your edits if this should happen to you.
Just visit https://www.tumblr.com/themes/recover! It’ll give you a little dropdown menu option for which blog you want to edit ( in case you have any sideblogs you’re using as well ) and will offer to revert your theme back to when your last html/customization edit was made, no matter how long or short ago it was.
I ended up having to use it, and all you’ll have to fix from scratch is your title and any symbols you have in your description/links. Please, please reblog this if you’d like to spread the word! It’ll save people tons of time if their blog gets wiped out and set back to default.