Well, that’s not entirely a foregone conclusion - as you’ve got an external microcontroller, you could give it the facility to interrupt the power.
I presume your current hardware doesn’t have such a capability?
It’s not uncommon to have certain parts of a circuit that are not “hit” by a reset signal - so, if anything goes awry, a power-cycle is required.
eg, memory doesn’t usually have a “hard” reset - it relies on software to initialise.
Sorry this doesn’t solve your problem, but it may be of some consolation to know that it’s not entirely unheard-of.
Are you in touch with SiWi about this…?