Customer reported this issue in Salesforce. I repro'd this issue in 4.25.3, 4.25.4, and 4.26. Therefore marking it as not a regression.
Renaming the variable something like "LifeTimer" does not result in this issue happening, it seems like it's just when the variable name is "LifeSpan".
Expected: LifeSpan variable stays set to 60.0
Result: LifeSpan variable is set to 0.0
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-102489 in the post.