After being confined to a matzah-based diet during Pesach (Passover), the Jewish people are happy to eat leavened products once more. A particular practice related to Pesach that some observant Jews have is that the Shabbat after Pesach, they bake what is called a shlissel challah (שליסל חלה), or "key bread." The reason why it is "key bread" is because the dough of bread is quite literally formed in the shape of a key.
Where did this custom originate? The oldest mentioning of it is from the Apter Rebbe, who was an 18th century Chassidic rabbi. In his work Sefer Ohev Yisrael, the Apter Rebbe provided various kabbalistic interpretations for the practice of shlissel challah. The Apter Rebbe's primary interpretation, just to give an example, is that after the Israelites brought the Omer offering on the second day of Pesach (Joshua 5:11-12), there was no longer manna falling from the sky. Sustenance was very much a worry, and is supposed to represent opening the gates of Heaven to listen to their prayers. When you look at the interpretations, they are loosely tied to the concept of a key, and do not establish a centuries-long practice that could possibly date back to Mount Sinai. This has evolved into the practice of shlissel challah. Some simply shape the bread in the shape of the key. Others put an imprint of a key in the dough, while others back a key into the loaf itself.
The first criticism is that the practice quite probably has non-Jewish origins. Shelomo Alfassa wrote a piece on how its origins are not Jewish in nature, specifically citing the Easter practice of "hot crossed buns" that dates back at least to the 15th century. He also pointed out that keys were traditionally in the shape of a cross, which is unsurprising given the fact that Ashkenazi Jews lived amongst Christians for centuries. Some have attempted to discredit Alfassa's argument, but there is another facet of Christian practice that Alfassa did not cover, and it has to do with hiding trinkets in bread for holidays. Just to give some examples of this concept from the Christian world that shlissel challah mimics. The Greeks bake a New Year's bread called vasilopita, which contains a hidden coin that is supposed to give good luck to the receiver. The Serbians have a loaf called cenisa, which is the same idea, except the bread is eaten on Christmas. The Bulgarians eat a similar bread to the Serbians on Christmas, as well, called a pitka. There are other non-Jewish practices where hiding trinkets into bread, e.g., king cake, which also predates the practice of shlissel challah. Not only does shlissel challah have noticeable parallels with these Christian practices, but these Christian versions even originate from the same region as the custom of shlissel challah, i.e., Eastern Europe. Also, if one considers Nisan the beginning of the Jewish calendar, then having good luck with one's parnassa for the remainder of the year draws upon yet one more parallel.
Even if you remain agnostic on the non-Jewish nature of the shlissel challah's origins, there is another issue to be addressed. The shlissel challah is seen as a segulah (protective or benevolent charm or ritual; סגולה) for one's livelihood (פרנסה), and regardless of the interpretation you accept, the practice of shlissel challah is based on the theme of פרנסה. Essentially, it's treated as a good luck omen for improved finances and career prospects. This practice has a similar problem that I have with the practice of swinging a chicken over one's head before Yom Kippur for the purposes of vicarious atonement. The issue? The Sages (חז׳׳ל) taught us that we were supposed to earn our keep. Given how the ultra-Orthodox tend to view antipathetically, should they culturally reinforce the idea that work is bad? Normally, I would take a more "live and let live" approach to religious practices. I would even be more accepting of it if those who baked the shlissel challah recognized that we can introduce new rituals into Judaism instead of this fundamentalist idea that everything in Judaism was quite literally given at Mount Sinai. (Spoiler: Judaism has evolved as a religion, it's not identical to what was practiced 3,000, 500, or even 100 years ago, Judaism has taken in foreign practices and ideas, all of which is okay because Judaism is meant to adapt). However, I take issue when it reflects deleterious social values, mainly that "G-d will take care of it, and I don't have to do any work," which is problematic in the ultra-Orthodox world both in Israel and in the Diaspora.
I'm not going to stop people from baking shlissel challah, both on philosophical grounds and because it would not be enforceable. However, I also believe that this practice is more than some innocuous placebo: I take issue when it reflects deleterious social values, mainly that "G-d will take care of it, and I don't have to do any work," which is a prickly issue in the ultra-Orthodox world both in Israel and in the Diaspora. Additionally, I don't like how G-d is treated like a vending machine. You don't metaphorically put in a coin in the machine, and a out pops out what you ask for and thinking you can alter G-d's will by baking shlissel challah. Baking a loaf of bread shaped as a key or a loaf with a key inside it is not suddenly going to solve your financial woes. Jewish culture has absorbed some superstitious practices (e.g., treating the mezuzah as an amulet, spitting three times), but at the same time, treating shlissel challah in a superstitious manner is a violation of Jewish law. There are other ways to become closer to G-d, but baking a shlissel challah is not one of them.