I have a space bar like this. The little tabs holding the stabilizer in place just weren't there on one side when I got it.
The easiest way to deal with it is to order a new one, either from Unicomp, Clicky Keyboards, or Fentek. Last I checked, they all sold them.
It will only cost a few bucks to do. Assuming you're in the US, anyway. In Europe or APAC, it would cost more due to shipping from the US, but I don't know of any source for parts that would be local to the EU, let alone APAC.