Using the math expression Atan2(y,x) inside of a math expression node results in an error.
Tested in: 4.23.1 CL#9631420 , 4.25 CL#11341939
Result: Error appears on the node, atan2 can't be found
Expected: Atan2(y,x) to work as an expression
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-88550 in the post.