Is the Holder or the Servicer responsible for servicing actions while servicing FHA mortgages?

Holders are responsible for all servicing actions, including the acts of its Servicers.
Servicers are responsible for their actions in servicing FHA-insured Mortgages, including actions taken on behalf or at the direction of the Holder.

Additional questions may be directed to the HUD National Servicing Center at (877) 622-8525.
See policy in Handbook 4000.1, Section III.A.1.b. at:

All policy information contained in this knowledge base article is based upon the referenced HUD policy document. Any lending or insuring decisions should adhere to the specific information contained in that underlying policy document.

Topic Number: KA-05207