Monsters spawning on normal farm

Version Info:

Windows 10
Installed Trough Steam
Version 1.3.27
BuildID 2978836 (Although it's possible it was updated since we played if a release has gone out since about 2018-08-07 2330 Pacific.)

I had previously opted into the Beta to play multiplayer early, but I'm not sure if I'm still getting Beta updates. The Betas setting on Steam says NONE now.

The Problem

I'm playing a multiplayer game with a friend, and last night, we suddenly got monsters spawning on our farm at night. Our farm is the Standard Farm type. It has only happened on one in game day. We got to the end of the in game day, allowed it to save, and then exited; we stopped playing because we were worried it would happen again and don't really want to deal with this right now.

Some specific info that may or may not be relevant:

• We are a day or two past the Night Market event in the 1st year.
• The night before, I passed out in the mines when the clock hit 2 AM. (This is by no means a regular occurrence.)
  
• We just finished the Pantry bundles on the day it started. The Greenhouse completed after the monsters appeared.
• We just turned in a Dwarf scroll to the museum. Again, this was on the same day the monsters appeared.
  
• We started setting up some sprinklers. The monsters even destroyed one.
• One of the monsters we killed seemed to be a Wilderness Golem. It was a golem graphically and dropped fiber. So it doesn't seem to be something like the monsters from another map mistakenly spawning on the farm.

We haven't unlocked the witch's hut to enable monsters yet, but we did confirm that the <shouldSpawnMonsters> element contains false in the save file. (I'm assuming that's the setting that controls it. I didn't see anything else that looked obviously related in the XML.)

Is there anything that could have triggered them spawning? Is there any way to stop it? This seems like a bug.

 

Also, if this is a bug, could anyone explain how we could modify the save file to get our Quality Sprinkler back? Iron, gold, and quartz aren't exactly effortless to come by.