This problem started in 4.24 and not in 4.23.
CL 9114926 seems to be relevant.
Import the FBX file into the project, and set the Normal Import Method of Import Setting to Import Normals and Tangetns.
It is correct when imported, but not when re-imported.
sample : [Link Removed]
The number of vertices changes with each re-import
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-87842 in the post.
|Component||UE - Editor - Content Pipeline - Import and Export|
|Created||Jan 31, 2020|
|Resolved||Mar 13, 2020|
|Updated||Jun 23, 2020|