I’m guessing that the Wemos has gone faulty, and that the Blynk.Air update is just a coincidence.
If the device was running okay and one of the internal pull-up/down resistors has failed then the next firmware update would fail, regardless of how it was delivered.
If you take a look at this post:
You’ll see which pins need to be pulled up/down to place the board into programming or run mode. As you can see, it’s not just GPIO15.