I tried reading through some of the other rules not triggering topics but none of them appear to be the situation that I have (that I can tell anyway). I suspect that the issue I'm experiencing is that I'm just being dense and I've set these rules up wrong. What I'm trying to do is set up lights to come on 45 minutes before sunset so long as that time is before 19:00. If we get to 19:00 and we're not 45 minutes before sunset then execute the rule anyway. I just want these lights to come on in the evenings at reasonable time without having to set up rules for the autumnal>vernal equinox and then another set of rules for vernal>autumnal equinox (which is what I had before, and worked).
If I trigger the rule manually at the correct time the rule runs fine. It will not trigger on its own though. I have a couple of other rules that will run just fine if I run the actions manually but they will not trigger based on the time/conditions. The logs are telling me nothing particularly helpful either. As far as I can tell, nothing happens. I've been using Hubitat for a while but up until recently I've just had some really simple rules.
There's no need to include the Trigger time and its restriction as a Conditional in the Actions section. The rule would not have fired if those weren't true, so there's no point in immediately re-evaluating them as the first action in the rule.
But you also have 1900 in that first Actions conditional -- I suspect that should instead be added as a second Trigger time? Otherwise, with the Trigger as it is now, 1900 will never come into play here since it's outside of the Trigger.
ETA - welcome to the community!
Second edit... If using 1900 as a second trigger is desirable, then that raises the issue of making sure the actions only fire with one of those triggers (but not both)... That gets thornier, and there are a couple options you could use... You could leverage a Private Boolean to act as a True/False gate at each time. Or you could do something like this...
Trigger: Time is 1500
Actions:
Wait for event: Time is SS-45 (Timeout 4 hours)
If Time is SS-45
Do stuff with lights
Else
Do stuff with lights
End If
The first IF covers the SS-45 timing between 1500-1900, but if SS-45 is outside of that window, then the ELSE kicks in at 1900 (after the 4-hour timeout expires) and it sets the lights.
I think that would work, anyway -- it's what I'd try.
Thanks to both of you! I had started off with something simpler than what I've show in the screenshot but it the rule still wasn't triggering and, if I remember right, RM was complaining that I had unused conditions. I've fiddled with this rule so many times now I've forgotten all the different iterations I've tried. I think I need to go back to something simple again, then try these suggestions. I'm going to give @user5298's suggestion a shot first as it seems relatively simple to understand what's going on if/when I have to come back to the rule for any reason.
Thanks! 
Just wanted to circle back and say that the suggestion from @user5298 worked and my problem is solved. Also, @user6610 your suggestion helped too because as I was looking at what you suggested (and was playing around with it) I discovered that on at least a couple of rules I had null required expressions (no idea how that happened) which was causing a couple of the rules to fail with "required expression now false". It wasn't until I was playing around with your suggestion that it dawned on me what might be going on. Thanks to you both!
Welcome to the community. Love your "...I must be missing something..." topic title. Story of my life.
FWIW, having unused conditions isn't a problem per se, if you created conditions and then decided not to use them. They won't hurt anything being there & unused. Generally you should remove them at some point as it keeps you from getting confused in a month when you look at the rule and wonder why you aren't using a condition.
