The messages that you see mention that due to a spanning tree topology change the switch forgets all learned mac addresses on the affected ports and starts learning which MAC is behind what port again.
Spanning Tree Protocol (STP; https://en.wikipedia.org/wiki/Spanning_Tree_Protocol) is an old method of preventing loops in your network. If you have connected your switches and you create a loop in the network (for redundancy, or unintentionally), the STP stops the loop while still having all switches connected.
In a stable network, there should be no topology changes, so as you see them please go and find where those originate from (use spanning-tree show and debug commands).
If you have just a stack (Arubastack), make sure that all stacking links are indeed stacking links (not regular network connections, with ports that show up in show interface brief).
If you are sure that there are no loops in your network, you may try disabling spanning-tree on the switch; but be warned, if someone creates a loop, your network may go down by broadcast storms.
The messages should be harmless, though if they appear frequently the unstable spanning tree may be harmful.
Not sure why you don't see mac addresses in the WebUI; what worked for me once was reloading the web-page when it was showing 'Please wait..'; after that reload is was quick.