This has happened to me twice now after the Gleaming Society fight in Longwatch Falls. After it some of my characters slow down, either in normal mode or in sneaking mode. The first time my main character couldn't even move at all in sneaking mode and was greatly slowed in normal mode. Unfortunately I don't have a save of that.
The last time I did it only Itumaak was slowed down. Now he can't keep up with the party when sneaking, which is rather annoying. I'm also reluctant to continue in case I get more of it on other characters. It also seems permanent since neither sleeping nor changing out characters in an inn seemed to fix it.
Edit: This is in 2.01. Forgot to add it to the title.
https://dl.dropboxusercontent.com/u/29865147/Haukionkala_PoE_saves.zip
output_log.txt
