I'm not sure exactly to what you are referring, except that Clair made quite a bit about the XXI being in bad shape and poorly designed / constructed.

As Germany began to use non-ship builders to make submarines, under the pressure of allied bombing, some of the quality of the late war boats suffered. The XXI - a revolutionary design put together in a hurry at the end of the war but which never saw service - reflects this. Many of the welds were poorly done, and some of the detailed engineering (the hydraulics etc.) was oddly done.

Repair and service work done in france, similarly, began to suffer in the later war years due to sabotage by french workers. (They didn't resist German rule in this way until it was clear that the Germans were losing the war, but that is another story....). This caused a number of patrol aborts and delayed sailings...I might add that the US had a number of patrol aborts due to fouled water and food - perhaps more % wise then the Germans, and sabotage was certainly not a suspicion.

But it is not fair to compare these 1944 - 45 construction jobs with the vast number of German boats, which were very well made, and could take a beating and keep on ticking. The allies were quite impressed with the U-570, and early war boat, when they captured it.