I think isn't a specific issue related to IPv6, but is a problem with VSX on Maestro.
In my company we've maestro setups with one security group each, some of them we're working with 3 vsx per sg, we faced some issues, where we need to reboot all SGMs simultaneously and this caused a huge impact for us.
The cases opened with TAC weren't able to find out the root cause, but they explained when a VSX is down, for MHO the whole SGM are considered down as well.
I've installed the HF81 for R81.10 last weekend and seems something was improved, since I didn't face any issue and in the same maintenance window, I created 2 new VSX.