Jen,
I will concur with Evan on this one. A spike that minor should not be cause for concern. However, knowing what happened to your last clutch, I know you are worried to death. Those eggs should be fine.

To clarify what D said, yes eggs willl start to generate heat towards the end of incubation. However, I have never noticed any of mine generate heat like that at day 40. Normally the box starts to heat up around day 50.

Hope that helps,