We have in Yiddish an expression for "what's the matter" that sounds like "was is der mehr?". Is this German or what? I can't make sense of it.
Admittedly I never heard this or any similar expression in German (not even unrelated to "matter").
What comes to mind however is the now unusual German "die Mär" (used in the meaning of tale, story, report, derived from Old Hig German mârî and also in its diminutive still used in "das Märchen").
By changing gender and thus article we could have said:
Nobody uses this expression nowadays but considering it's ancient roots in the German language it may well have survived in Yiddish.