The troop ship is showing up in the ship drop-down list filtered for troop ships. I did a print-screen showing "executioner #10" which is the ship shown in my first print screen.
The only thing I can think of is that there might not be enough troops to load. I went back and counted available troops that were at 100% and not loaded, and I had 14 of them. Each of my toop ships has three ETC TS-200 troop carrying compartments with capacity 130, hence 390 total (or 3 full troops at 100% and and a 90% "partial" troop .. probably should've put 4 of them to get 520 capacity or 5 troops as 100% .. I'm assuming that's what this means because I'm not sure). I counted 5 troop ships loading, thus that would be one less from the 14 troops I have at 100% (5x3=15). Maybe this is why the other leftover troop ships do not have the "load troops" option in the drop down menu? because there are not enough troops at 100% ?
If that's the reason, then not having the "load troops" option is confusing; it should have an "insufficient troops available to load" error message so that the player understands why and not just a missing menu option that should be there .. gives the impression that there might be some other (or many other) reasons.
Of course, this is assuming that this is the reason for the missing menu option. It could be something else I'm unaware of entirely. This is only my 4th game and the first one that I'm using troops. I'm basically just guessing here based on the info I've got and what seems reasonable.
Not tho' the soldier knew
Someone had blunder'd:
Theirs not to make reply,
Theirs not to reason why,
Theirs but to do and die: