Reproduced 3/3 times, issue also occurs in //UE5/Release-5.0 - CL 20979098 Binary. Confirmed NOT a Regression.
No memory leak occurs when watching a new blank Actor BP, which implies the root cause is from the Pawn BP.
Actual Result: You can see a gradual memory leak coming from the editor. On more complicated pawns (including new blank Character BPs) the leak is even faster.
Expected Result: No Memory Leak
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-171618 in the post.