Short answer:

We don't have detailed numbers for casualties of the Black Death by ethnicity, but what we do know suggests that we should be skeptical of your "multiple professors" and their unattributed story.

Discussion:

You know who else had similarly elaborate protocols of "religion-required hygiene" at this time?

Muslims.

If the hypothesis is "Religion required hygiene offers protection against the plague" -- well, the experience of the Muslim world with plague stands as good evidence that this proposition is false. While some aspects of Jewish and Muslim religious health practice, like circumcision, do have a demonstrable protective effect with some diseases, hand washing doesn't stop plague carrying fleas from biting you (how you get bubonic and septicaemic plague, pneumonic can be transmitted person to person) and we don't have evidence of any disparate survival.

The Islamic world being physically separated from Christendom allows us to ask: "Were the lands of Islam protected from the plague when it ravaged Europe?" The answer is "no" - Michael Dols is the scholar most closely associated with a study of plague in the Islamic world, his observation:

[E]pidemic cycles in Egypt and Syria may be compared to those in Europe. In France, from the Black Death until 1536, there were sixteen principal epidemics that took place approximately every eleven to twelve years; plague has been documented for 176 out of 189 years. For Europe in general in this period (1347-1534), there were seventeen major epidemics that reappeared about every 11.1 years ). Despite the lack of detailed documentation for each area, the cycles of epidemics in the Middle East and Europe appear quite comparable

Moreover, the plague continued to devastate the Middle East long after it had abated in Europe-- there are outbreaks of plague in the region in the 18th and 19th centuries. One might add that we don't see reports of differences in plague incidence between Christians and Muslims in the Islamic world-- there were many plagues in Egypt, and Coptic Christians aren't reported as more affected than their Muslim (or Jewish) neighbors.

Beyond that, we should be wary of the "Jews were magically protected" lines of argument, because they are the flip side of the "Jews are magically culpable" blood libel. Jews were often blamed for plague and other misfortunes-- far from being "protected from plague", the evidence we have is that Jews were likely to be blamed for plague even before it broke out; in the Rhineland for example it seems likely that murder would be a more likely cause of death than plague-- not reflecting any hygienic protection, but rather the malice of their neighbors

[L]ess attention has been devoted to the most monumental of medieval Jewish persecutions, one that eradicated almost entirely the principal Jewish communities of Europe - those of the Rhineland along with many other areas. Coupled with mass migration that ensued, they caused a fundamental redistribution of Jewry. These persecutions were the burning of Jews between 1348 and 1351, when in anticipation of, or shortly after, outbreaks of plague Jews were accused of poisoning food, wells and streams, tortured into confessions, rounded up in city squares or their synagogues, and exterminated en masse.

We have evidence that people with the best access to information at the time, such as Pope Clement VI, did not see any disparate survival of Jews

It is true that some at the pinnacle of power, such as Duke Albrecht of Austria (at least initially) and especially Pope Clement VI, seem to have risen above the hysteria, seeing the violence against the Jews as irrational and dangerous to Christian society. Early on, Clement promulgated Sicut Judeis (26 September 1348), which argued that Jews were dying in numbers as great as the Christians, and that they would not have been so stupid as to poison themselves

While our demographic data for the plagues of the 14th century is poor, the data get better for later plagues. Writing of the plague in Venice in the 16th and 17th centuries, where Jews were confined to the Ghetto [Weiner:1970] can say

[Regarding the] plague which struck Venice between 1575 and 1577. The number of Jews in the Venetian population declined from a little over ten thousand to a little over one thousand. In percentage terms, this was a decline from over five to under one per cent of the population.

This does not suggest any survival "advantage" -- quite the contrary.

Finally, one might observe that plague has often been thought to have been more prevalent in cities, and Jews were a more urbanized group. While we don't have good numbers to say much of anything quantitative about survival of Jews vs Gentiles, we _can_ say that Jews were more likely to live in cities or other conurbations; and if as some suspect plague deaths were greater in cities, that would imply a higher not lower mortality. When plague came, people are often reported to have fled to the countryside, perhaps with good reason. This is a topic of current historical inquiry; scholars such as [Curtis:2016] suggest that at least in some places and times with more densely settled agricultural areas like the Netherlands, plague could be as devastating in the countryside as in cities.

Sources:

Dols, Michael W. “Plague in Early Islamic History.” Journal of the American Oriental Society, vol. 94, no. 3, 1974, pp. 371–383

Dols, Michael W. “The Second Plague Pandemic and Its Recurrences in the Middle East: 1347-1894.” Journal of the Economic and Social History of the Orient, vol. 22, no. 2, 1979, pp. 162–189.

Dols, Michael W. "The Black Death in the Middle East" (Princeton:1977)

“TOWARDS A NEW UNDERSTANDING OF PLAGUE AND QUARANTINES IN THE OTTOMAN EMPIRE.” Plague, Quarantines and Geopolitics in the Ottoman Empire, by BİRSEN BULMUŞ, Edinburgh University Press, Edinburgh, 2012, pp. 177–180.

Theilmann, John, and Frances Cate. “A Plague of Plagues: The Problem of Plague Diagnosis in Medieval England.” The Journal of Interdisciplinary History, vol. 37, no. 3, 2007, pp. 371–393.

Cohn, Samuel K. “The Black Death and the Burning of Jews.” Past & Present, no. 196, 2007, pp. 3–36.

Curtis, D. R. (2016). "Was Plague an Exclusively Urban Phenomenon? Plague Mortality in the Seventeenth-Century Low Countries". Journal of Interdisciplinary History, 47(2), 139–170.

WEINER, GORDON M. “The Demographic Effects of the Venetian Plagues of 1575-77 and 1630-31.” Genus, vol. 26, no. 1/2, 1970, pp. 41–57.