minecolonies-universal-1.12.2-0.8.7719.jar
forge-1.12.2-14.23.2.2624-universal.jar

The closest blowing was at 82 blocks from the center (the one you see on the 2nd picture), which apparently is considered outside the colony. The visualization line is at 143 blocks from the center in the shortest way. And yes it's in SMP.

Can you check if those areas show your colony in f3?
Is this in SMP?
Is this close to the SMP spawn?

@lebanni Could you please update to the latest Alpha and verify if this is still happening to you.
Else this issue will be closed as resolved.
Thank you.

It's seems to work fine now. But I had to start a new world. I'll see when I have guards again. In the meantime I think you can close the issue.