I have tested this issue on several devices and can't replicate it，updated V003 to V007 via OTA,and tried V004 to V007 via OTA,turn-on ROOT,or Turn-off ROOT.Are there any special procedures or requirements?
It might be of interest to take into consideration what @Pingouin wrote in #21 above. The same exact thing that he reports happens when I try to replicate the situation. There is always a black screen lasting for some minutes in which I thought, for the first time, the box had stalled. Fortunately I resisted the urge to pull the power cord and so it progressed smoothly after what seemed like a long wait. I wonder if there might be some boxes in which this doesn't happen as for me it seems to be default for this update.