I've had several routers on which the bridges have gotten deleted somehow. Each time, the router had a bridge with Ethernet and WLAN ports on it. Users would report loss of connectivity, and when I logged into the router, the bridge was gone. The ports showed to be configured for a nonexistent bridge with a name consisting of an asterisk and a number - for example, "*8." The IP address that was assigned to the bridge also gets assigned to bridge *8. Bridge *8 doesn't really exist on the router, but the ports and IP address get assigned to bridge *8. When I create a new bridge and change the bridge interface for each port from *8 to the new bridge, and assign the IP address to the new bridge, users regain connectivity. What would cause bridges to get deleted, and cause ports and IP address reassigned to *8?

You have applied all updates?

What is the hardware and RouterOS version?

It is 6.42.6.

What hardware?

I've seen it on hAP and RB751.

Related topic (yet unresolved): viewtopic.php?f=2&t=138323

Using new VLAN Bridge ROS >=6.41, you only need one Bridge to solve everything.
Se bottom of my post here:
viewtopic.php?f=2&t=138232

I've seen it on hAP and RB751.

Depending on router configuration, I have seen cases where the auto conversion of the bridge does not work properly from pre-6.41. If the bridges disappeared on upgrade from versions below 6.41 then it might be due to this.