My assumption is that it will always be a problem.

There was a case in Virginia where a man was killed by a US civil-war era artillery round in his garage. Granted, he was in the process of making it safe at the time, but this was ~2010 from memory - so ~150 years after the conflict occurred.

Given that, we can obviously expect that some ordnance from WW2 will still be dangerous in 2095.