Goblin raiding parties disappear into ground

shortly after receiving the alert that “a goblin raiding party” is approaching, the party in question will randomly sink into the ground and the game acts as if they left or were killed.

Steps to reproduce:

  1. wait for alert to appear (starts happening after tribute is asked for and refused)
  2. click on alert to focus on party
  3. no other action is required

Expected Results:
soldiers come and defeat enemy

Actual Results:
enemies disappear, no interactions between them and hearthlings required

Notes:

Attachments:

Version Number and Mods in use:
alpha 19 release- 687 (x64)

System Information:
windows 10