How To Move Ai Characters To The Nearest Actor

Hello,
In My Ue4 Project I Want To Make My Ai Characters Move To Nearest Actor (RealBuilding)
So I Made A Reference To The Nearest Actor From Every Ai Character
This Is My BP Image To Make The Reference

And The Reference Worked Will,
After That I Wrote This Node To Make My Ai Character Walk To Nearest Actor

The Ai Characters Walk To Nearest Actor Perfectly

The Problem Is When I Remove(Destroy) Any Of The Actors That The Ai Character Have A Reference To,
The Ai Move To The Location Where The Actor Was Before I Destroy It
And I Don’t Want This

The Second Problem Is When I Add Another Actor (RealBuilding) Next One Of My Ai Characters The Character Doesn’t Move To Any Actor They Just Play The Idle Animation
I Think That The Problem Is When The Reference To Nearest Actor (RealBuilding) Changed The Ai Character Will Not Move, And If The Reference Destroyed The Ai Will Finish The Node And Walk Into
The Location Which The Actor (RealBuilding) Used To be There And After That The Ai Character Will Not Move To The New Reference
Or Move To Another Actor (RealBuilding)

So If Any One Have Any Ideas Please Tell Me

Thanks.