The input removed the connection points are not re-indexed. So connected 'wires' stay on their places. That causing disconnection of the last wire as well as shift for every node that followed the one being removed.
Found in 4.19 CL# 4033788, 4.20 CL# 4302132, 4.21 CL# 4307852
What was attached to the 4th input will be disconnected and attached to the 3rd
What was attached tot he 4th input will stay connected and disconnect the 3rd input
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-63363 in the post.