There are 3 pairs of SRBs. The central pair lasts longer than the other 4 and they have radial simmetry x2, but one of them consumes all the fuel faster than the other.
I thought this was related to the bug where chamging engine parameters is not duplicated in the simmetric engines, so I deleted one of the SRBs and made the simmetry from zero, but the problem persists.
To control the craft just activate the first stage and wait
@RenxBlake your bug seems to be related to this one instead of my report, thank's for reporting it :)