I have not run into this issue, but that is a HUGE upgrade from 10.1.06T to 10.1.15T and from 08.0.30t to 08.0.90a. I generally always upgrade code before deploying new devices and at regular intervals, and I am certain more testing has taken place between each build family and the next build family of code.
Most of those didn't even ship from the factory with 08.0.30 builds but rather 08.0.60 originally, which doesn't support stacking... until 08.0.61 builds.
I would make sure you are in configure terminal when you tell it which flash image to boot. Then do a "write mem" before reloading.
Did you validate that it copied the image to all devices by doing a show flash?
Personally, I would probably jump build families in stages going to say 08.0.61x... Being sure everything works and saving the configuration again.
Then I would then jump to the 08.0.70 builds. Each family runs a pre-parse script and converts and changes the configuration a little. I am not 100% sure that 08.0.90 builds can pre-parse 08.0.30 configurations being how different they are for things like LAGs, Dual-Mode, and PoE
Honestly, it might be easier to export your configuration and compare it against your template to make everything you need for a clean reconfiguration.
Maybe someone from Ruckus can chime in on this.