I think there is a bug when selecting signals in Train conditions. When you add a circuit condition to a train schedule, when you want to select a signal and you press a tab to find the item, you can "multiselect" the tabs, but you don't actually go to the tab. You can still search for the item like "Green signal", but you cannot do it via the tab.
Here is a screenshot with six tabs selected: https://imgur.com/wIRcb1z
I use mods though, but it started since the GUI update.
[0.18.13] Cannot select items in "circuit condition" in train schedule
Re: [0.18.13] Cannot select items in "circuit condition" in train schedule
Fixed in Version: 0.18.15.
Thanks for the report.
Thanks for the report.