Your BH adventure score should never drop. That part is a bug, IMO. Not sure if it's just visual (i.e., in the end you get the correct score) or more serious. You can check that when I explain how this score is computed.
First, a bit of Plraium terminology: basic points of a unit are
- off points for offensive units,
- average def points (i.e., the sum over all 4 types, divided by 4) for def units,
- scouting points for scouting units,
all taken into account without any bonuses. For example, a Bonnie has (20+20+18+18)/4 = 19 basic points, regardless of relics, discovery upgrades, prestige, haven def, potions,... anything! A Marauder has 40 basic points.
These are the points that FSs fight against, for example (so, a FS can kill 12600/19 = 663 Bonnies or 12600/40 = 315 Marauders if they are alone).
Back to your question: for a "training" BH adventure, your score is the sum of basic points for all the troops you put in the oven (plus those you revive, I think) divided by 40. That's all there is to it, nothing more. I know, kinda anticlimactic. ;-)
Anyway, a Nautilus has (600+750+1275+900)/4 = 881.25 basic points, so 20 Nautili have 20*881.25 = 17625, giving you 17625/40 = 440 points. Looks to me like you trained 40 Nautili (not just 20) to get to 881.
Next, an Orni has 1140 basic points, so 10 of them will give you a score of 1140*10/40 = 285. Add that to 881 you had before and it's 1166.
Adding 20 Aquanauts should've given you 150*20/40 = 75 points, getting you to 1166+75 = 1241.
Etc.
If you go through this to the end, you'll see how much you should've gotten. If the end result is severely wrong, you might want to submit a very detailed ticket (like your original post, with any further details that you can add).
I hope this helps you.