After playing AH3 (new version) for several hours I start to get many unable to open .../settings/[some config file] when attempting to do various things, like show downtimes. The file in question often seems to not be relevant to what I was doing at the time. Once I get one error, then all subsequent actions lead to errors as well. The problem rises essentially every time I play for several hours at a time. Several other people mentioned the same thing happening to them, but I couldn't find any mention of it in the Bug Reports using the Search feature. Restarting AH3 fixes the problem.
(If relevant, I have AH3 installed on an SSD.)