I had a miscellaneous quest titled "Find the laser in Fraternal Post 115." I went to check it out and killed all the super mutants. Once the last one was dead, a notification popped up saying that the quest had been completed. However, I don't see anything new in my inventory and I can no longer view the quest on my Pip-Boy. A thorough search of the area did not turn up a laser, either.

Has anyone else encountered this? If so, do you have any information about it?

It's just a random quest. I had one that was find the Combat Rifle in the same hospital that is the end of the Silver Shroud questline.

I literally found a Combat Rifle (as in stock CR, nothing fancy, not even legendary status) while looting the place. Quest complete.