My internet provider provides IPv6 via prefix delegation (DHCPv6). I'm getting a /60 network.

I successfully set up an address pool (prefix size /64). From that address pool, I want to create two /64 networks.

First, I created a network for all devices that use SLAAC:

/ipv6 address add address=::1 from-pool=isp-v6-pool interface=bridge advertise=yes comment="Main IPv6 net"

Then I added a network for devices that will be configured using a static IPv6:

/ipv6 address add address=::1 from-pool=isp-v6-pool interface=bridge advertise=no comment="Server IPv6 net"

This works, both /64 networks are created. However, when I reboot the router, only the first address is still around, the second is gone. On the device with the static IP, routing stops working when rebooting the router.

The only difference is that the second net uses advertise=no. Is that the reason? Or could it be a bug? (Note that I'm still quite an IPv6 beginner, so this might be some kind of conceptual misunderstanding on my side.)

RouterOS version is v6.47.2.

Does nobody know anything about this problem? It feels like a RouterOs bug to me...

The only difference is that the second net uses advertise=no. Is that the reason?

No

I'm scratching my head over trying to assign two /64's from a pool to the same interface. Very suspect over that being a valid configuration. I get a /60 and assign to multiple physical/vlan interfaces as such:

This works, both /64 networks are created. However, when I reboot the router, only the first address is still around, the second is gone. On the device with the static IP, routing stops working when rebooting the router.

Generally it doesn't make much sense to give device multiple addresses from different subnets on the same interface. I mean that devices from different subnets won't communicate directly with each other because they are not supposed to and traffic will pass router anyway, so why not making the right thing and separate them to two subnets (can be VLANs). OTOH just to have some device static address set it is not necessary to create a separate subnet for it...