This is actually a Switchvox question -- but I was directed to this being an Asterisk problem, so please excuse me if I'm making rough guesses at what is happening internally (I've configured bare Asterisk systems before, but have no clue what Switchvox is doing internally).
So in Switchvox 5.x I had an IVR where we set a variable, then called a web request. If the web request timed out, or the web request returned a blank/missing entry for the variable, it kept the old value, this allowed us to have "defaults" for the very rare instance that our web services would be down.
In Switchvox 6.x it will now set that variable to "null", which is a massive pain, Switchvox has no way for checking for "null" and in order to set a variable on a conditional I must jump into an IVR to do the switch, then jump back into my original IVR, it's a huge pain, and creates a very messy IVR.
The engineer I talked to said that the Asterisk versions were changed between 5.x and 6.x and this change was internal to Asterisk, so I'm elevating here to see if there is a reason for this change, or if it was an unforeseen side effect, and maybe see if some Asterisk engineers can't discuss this with the Switchvox team (or at least create IVR tooling for us to be able to support this new workflow). It makes systems automation with fallback a huge pain (and HA isn't really on the table for the services as of this time).
It's case #00635556 at Digium, let me know if I can provide anymore help.