"If you ever compile a Blueprint that you have opened in the Property Matrix, it will lose its connection and variables you change in the blueprint won't be reflected in the Matrix and vice versa leading to a indeterminate state of what gets saved when you save the Blueprint."
Confirmed in Main @ CL 4845042
Result: Properties are no longer mirrored
Workaround: Close and reopen the property matrix
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-69348 in the post.