Petra

Drink it as espresso, which it is good at. Also check the bag for a roast date rather than a best-before: a kilo bought at once is a lot of coffee and stale oils taste flat and papery and ashy in their own right, which would compound what the roast is already doing.

Both are plausible and your own observation points at the roast. Very dark roasts, the ones labelled French or Italian or espresso, develop smoky carbon-like flavours. In hot coffee that reads as bold. Cold brew is smoother and much less acidic, so there is nothing to balance the ashy notes and they stand out.

So the same beans being fine as espresso is not a contradiction, it is the explanation. Try a medium or medium-dark for cold brew; chocolatey nutty mediums make much better cold brew than anything labelled Italian.