Mom experiences pain when nursing home uses the Hoyer lift to move her from bed to chair. Has anyone else experienced this?

My mom had a stroke in 1981 that left her paralyzed on her right side. She is currently at the point in her care where she requires the use of a Hoyer lift to transfer her from bed to wheelchair. However, I just learned that she screams in pain while she is being transferred. Once she is in the bed or chair, she is okay. I hate seeing her in pain, but also don't want her to be in bed all the time - which is what is starting to happen. Has anyone had a similar experience? If so, did you learn what was causing the pain? Thanks in advance.