Turn off temp addresses. If your prefix changes then use ULA addresses.
Windows in powershell:
SetNetIPv6Protocol -UseTemporaryAddresses Disabled
SetNetIPv6Protocol -RandomizeIdentifiers Disabled
Linux: sysctl net.ipv6.conf.all.use_tempaddr=0
or in NetworkManager config file: ip6-privacy=0
OpenBSD: ifconfig em0 inet6 -temporaryI think a lot of people assume privacy addresses are required. You can just not mess with them. Privacy is dead anyway.