Relative forum links.
For whatever reason, direct links within the forum do not redirect between the US/UK/IE sites. If I copy and paste a link to, say, https://www.funimationnow.uk/forum/category/14/the-suggestion-box then anyone who clicks it will be taken to the UK site where, if they are in the US, they will no longer be logged in.
This could be avoided if there was some way to automatically convert local links to relative ones. This can be done manually (like so) but this is a faff and most users won't know how to or won't bother.