A nasty bug ! That seems worthwhile writing down.
I got a ‘not found’ error on @openzeppeling URL’s when developing an NFT. No callback. WTF ? I spent half an hour trying to find out what I was doing wrong. I was just doing a tutorial, I was doing everything according to the tutorial, and countless others have succeeded where I miserably failed. So I assumed I made a mistake, and spent half an hour double checking everything, reinstalling @openzeppelin/contracts, updating hardhat.
But no matter what I did, the bug happily persisted.
An African on Youtube had a solution, a friend of his had mentioned that to him. According to his friend, the bug comes from the Solidity plugin of VS Code.
If you install the v0.0.135 version (it is now at v0.0.163) the bug is gone. Just find the plugin through the sidebar plugin menu, click the uninstall button and it drops down : you can choose to uninstall, or install a previous version. Pick the latter and install v0.0.135. Reload the environment (ctrl-shift-p, reload window) and you’re good to go.
It is more of a workaround, it doesn’t fix any bugs, but at least you can work on and compile the source.