For that particular one, what tier in Frontline did you obtain?
452751-377751=75000.
Actually - you tiered up in all those reports... so that's probably it. You got 75000 for the tier up.
The others gave:
50000
25000
50000
50000
Which all matches tier ups.
I guess that solves it - it's not WG or anything being stupid - it's just your "Total amount for battle + Tier up reward = Credits earned"