After updating from 7.20.8 to 7.21.4 I had the issue that MAC addresses hang on their old interfaces after migrating the MAC address to another interface (for instance when live migrating a VM).
This issue sadly also occurs on 7.21.5.
I run 2 CRS309's using MLAG with a bonded MLAG peer port.
Is your VMM configured to send GARP on move?
Which VMM are we talking about here?
(I moved your post because this is not on-topic for the release thread. Only items related to documented changes are allowed in those threads. An absence of a wished-for change is not one such.)
The VM Migration is a live migration done by QEMU-KVM (Proxmox VE). I've used tcpdump on another node to generate a pcap and I see gratuitous ARP coming in from the VM after the live migration is finished.
I have run into a similar issue on CRS326-24S-2Q routeros 7.21.5 LTS. 2 switches with MLAG. Proxmox migration during reboot of a proxmox node. VM migrates off rebooting node, then back on, which leaves it unreachable due to some MLAG/mac address table stickiness. I've been rebooting the switches to fix it.
Spotted recent 7.24rc3-arm64 changelog https://mikrotik.com/download/changelogs?channelFilter=testing
*) bridge - fixed MLAG MAC address handling issues related to aging, flushing and moving (additional fixes);
Hopefully this is addressing the problem and it makes it into the LTS release soon.
This will get into LTS ... as soon as 7.24.X becomes LTS.
In Mikrotik world, version names (such as LTS, stable, ...) are only temporary labels to some particular versions .. and labels get moved with evolution of ROS versions. I'm pretty sure that this fix will not get back-ported to current LTS 7.21.Y.