I think this might be an issue with Gravatar and not Stack Exchange. I'll explain my reason for thinking this later in this answer.
First off, there is possibly a way to get your old gravatar back, adapted from Caleb's answer on Meta Stack Exchange:
- Go to the Wayback Machine.
- Enter the URL for your profile page. If you're lucky, it's been archived there. Go to one of the previous archived versions with the "right" gravatar and save a copy of your profile image from there.
- Edit your profile page and manually change your profile image to this saved one by first uploading it.
As for why I think this is a Gravatar issue, for interest, I looked at your case.
- The URL of your profile image as it appears in your profile is
https://www.gravatar.com/avatar/fd9e6c1e2c743da81cffdda6b01985f0?s=328&d=identicon&r=PG&f=1
- I found a copy of your profile on the Wayback Machine from March 8, 2016. The URL of the profile image from that page is
https://web.archive.org/web/20160308085014im_/https://www.gravatar.com/avatar/fd9e6c1e2c743da81cffdda6b01985f0?s=328&d=identicon&r=PG&f=1
So the Wayback Machine archived a copy of your avatar from that date, and the URL associated with the gravatar is the same as it is now.
In case people are seeing different things than I am, here are the two images I see:
The really important part here is the string fd9e6c1e2c743da81cffdda6b01985f0
which is the MD5 hash generated from your email address plus a little salt. Since the two hashes are the same, Stack Exchange has not recently altered the salt and you've not changed your email address (or at least the two changes magically cancelled each other out in an extremely unlikely scenario), so they are getting the gravatar from the same place. But the archived copy of this image is different from the current one. This suggests, to me at least, that the Gravatar identicon image for this hash has somehow changed, and likely that Gravatar has altered the algorithm for generating identicon images.