Some may have still been in relatively good condition but it in all likelihood, those that remained would have only done so where the land was of no particular use. Those trenches that were dig in what was previously farmland were most often filled in so that the land could be farmed again. While I can't say for certain, none of the texts u have looked at have ever mentioned the reuse of WW1 defensive positions.

The explanation for this is quite simple. WW1 defensive positions were completely inadequate for WW2 technology and tactics. We can examine the failure of the Maginot Line for an explanation for why this may have been. The Maginot Line was constructed in the interwar to prevent another invasion German invasion of France. The design of the Maginot Line reflected the experiences of the French Army during the First World War, a largely static conflict (at least in the French experience) that relied heavily on artillery. The problem for the French was that WW2 was not going to be a static conflict. Technological advancements in combustion engines which made tanks far more reliable and effective as well as aircraft rendered static defences obsolete. After the German advance through the Ardennes, the Maginot Line itself came under attack. The garrison was ultimately defeated and forced to surrender. Considering the elaborateness and strength of the Maginot Line and the relative ease the Germans had in overcoming it, it is doubtful that are-occupied First World War positions could have fared even a fraction as well.