Why do you have spanning tree enabled at all? If you have a plan for it and only activate it on ports where you need it, that's OK, but just spraying STP config on all ports "just to be safe" is NOT safe, specifically because of the problem you're seeing and more. More on that below.
To solve the issue at hand, set the desired root switch to bridge priority 0. That is not a 100% guarantee that it will remain the root bridge as that also depends on the system MAC address, but it is way better than having the standard 32k. Depending on your other config, this would do the trick:
configure stpd s0 priority 0
This WILL most likely cause a recalculation of your spanning tree, but that is unavoidable. Plan for it and do it when it does not cause too many problems. Sometimes you can minimize the problems if you disable all redundant links first. To make that easy, disable the ports that are already blocked by spanning tree as of now. Of course you need to make sure that this will not break anything when you move the root bridge role to the central switch. Then change prio as above, and lastly, enable the disabled ports one by one.
Here is where you decide if you want to use STP edge port functionality or ELRP. I'd go for STP edge port as it will cover some cases where ELRP will not work. Lastly, disable STP on all ports that are not edge ports (=access ports) or actually participate in a spanning tree ring. If you actually need to build another STP ring, enable it on those specific ports.
