So, I've connected a Mikrotik CRS326 Switch to a FritzBox router which has IPv6 properly set up.
Thus, the FritzBox acts as an IPv6 router.
The problem I have now is that SLAAC doesn't work for hosts that are connected to the Mikrotik CRS326.
In contrast, if I directly connect one of those hosts to the FritzBOX then SLAAC works.
If I replace the Mikrotik CRS326 with a managed Netgear switch then SLAAC works, as well (i.e. for the hosts that are then connected to that Netgear Switch).
Thus, it seems that the Mikrotik CRS326 somehow messes with IPv6 multicast and/or ICMPv6 which is required for SLAAC.
Is there some RouterOS configuration setting to tweak such that the Mikrotik switch just forwards (on layer 2) the IPv6 SLAAC packets?
Additional information: the CRS326 has pretty much default settings, i.e. RouterOS installed (updated to latest stable, though), all ports are part of the one default bridge/switch. There are 2 VLANs (configured via '/interface bridge' and vlan-filtering is enabled) and the FritzBox is connected to an untagged port.