You cannot change the intensity by just adding/changing numbers. You have to completely retype the entire value.
Found in 4.21 CL# 4613538 and 4.22 CL# 4681912
Results:
The value will return to 300
Expected:
The value would change to 200
Workaround:
Delete the entire value before inputting the value you want
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-68074 in the post.