How to handle toddler's long-term favoritism toward one parent

We're at our wit's end with our 20-month-old daughter, who almost since she was born has favored me (her dad) over her mom (my wife). Our daughter consistently chooses me over her mom in ways big and small, including regularly running to me and giving hugs but rarely doing so for my wife, and refusing to let her mom put her to bed or even get her dressed. For months, when I left for work, my daughter (who stayed home with my wife) screamed bloody murder, and even now I have to do a very focused goodbye routine to keep her calm.

Recently my daughter has entered a separation anxiety phase, and she'll often wake up in the middle of the night crying for me (almost never my wife). If my wife if she comes in to help, our daughter will push her away violently, sometimes clawing at or biting her. On the other hand, when I go in, I have the opposite problem -- our daughter will only stay calm and fall asleep if I remain within sight of her and don't make the slightest indication that I'm trying to leave the room.

I've tried to find advice online about what's causing our daughter to act this way and how to help her become less obsessive with me and more attached to her mom. I've been frustrated that most of what I've found is some variation of "it's only temporary" and "don't take it personally." This is a long-term issue, and we don't take it personally -- though obviously it's a very emotional issue for us.

It's not about differences in how we treat our daughter: we are both very loving parents, and neither of us are significantly stricter or more permissive than the other.

I also don't think it's a matter of how much time each of us spends with our daughter. While my wife stays home with our daughter part of the week while I leave for work, I usually handle most bedtimes and overnight issues (for the reason stated above), and we are all together most nights and weekends.

Any help, advice, or insight about how to proceed would be greatly appreciated!