There was some network disruption yesterday, likely due to current events increasing the demand on ISPs and Steam. This should have resolved on it’s own - see if it’s still occurring today.
This thread was added on March 26, 2020, with posts from FatsharkJulia.
Please contact your ISP, it may be due to network disruption or port blocking. Please see #7 here: https://support.fatshark.se/hc/en-us/articles/360021232734--PC-How-to-resolve-Sign-In-Timeout-errors