Intense load and stuck workers because of ladder

Summary:
my game loading bar was always full no idle but no errors or hindering so i didnt really bother, when a couple of workers kept walking up and down the ladder i decided to remove te ladder and replace. after i did that my loading went back too 80% idle. heavy load because of ladder? the load was partly filled with bfs
Steps to reproduce:
i have no idear how to reproduce.
Notes:
workers “stuck” on ladder kept switching item to backpack to hands like they got another order everytime they came up the ladder
Attachments:
bug code: 7797c20e-19e2-11e6-a30a-74d435ebcde8
Version Number and Mods in use:
no mods,
version develop-2972 (x64)
System Information:
i7-4790k
16gb RAM
gtx 980 4gb