Converted mobs always have their rotation set to 0,0 (south) after converting.
Reproduction Steps
Do
/tick freeze
Spawn a piglin
Do
/tick step 300t
Once that's done do
/tick step 1t
Observed Results
The mob loses whatever rotation it had and starts facing south
Expected Results
The mob would keep its rotation data
Linked issues
Attachments
Comments

My bad this is a duplicate of MC-248587