I think it is a race condition when there are bases on the map & the plugin is unloaded whilst they are active...
Only seen it with multiple bases.
After further investigation......
It seems to be client related.... I'm going to investigate if it is just 1 client that can see it or all of them....
but leaving the map & re-entering it, clears the issue, so I would say it's not permenently marked in the server.. but a client glitch...